Vulnerability-Lookup

CVE-2026-99281 (GCVE-0-2026-99281)

Vulnerability from cvelistv5 – Published: 2026-11-07 14:08 – Updated: 2026-11-07 14:08

Title

tun: Require CAP_NET_ADMIN to attach to an ownerless device

Summary

In the Linux kernel, the following vulnerability has been resolved: tun: Require CAP_NET_ADMIN to attach to an ownerless device Twenty years ago I made creating a tuntap device require CAP_NET_ADMIN in commit ca6bb5d7ab22 ("[NET]: Require CAP_NET_ADMIN to create tuntap devices.") The idea was to allow the permissions on /dev/net/tun to be relaxed to 0666 and thus allow owners of tun devices assigned with TUNSETOWNER to actually open it and get at their devices. What we missed at the time was that persistent devices with *no* owner were already essentially world-consumable, and anyone who could open the device node could also attach to those. Even then, using persistent devices with no explicitly set owner — on the (false) presumption that CAP_NET_ADMIN would be required to open them — wasn't an egregious userspace bug. There are cases where it does make sense to separate the creation/configuration of the netdevice, from the process which shovels packets into it. Since then, TUNSETGROUP was added a year later in commit 8c644623fe7e ("[NET]: Allow group ownership of TUN/TAP devices."). Its commit message noted that if both uid and gid are set, both have to match (in itself a bizarre choice) — but still not that with *neither* set, no permission at all was required. Then in 2012 commit c8d68e6be1c3 ("tuntap: multiqueue support") allowed new queues to be attached to a device from the moment of its creation, with no way for userspace to close the race between creation and a subsequent TUNSET{OWNER,GROUP}. In 2024, commit 3ca459eaba1bf ("tun: fix group permission check") tried to fix things to be saner: only require the user *or* the group to match, in line with standard POSIX permissions, and require CAP_NET_ADMIN if neither the user nor group authorised the access (although it put the CAP_NET_ADMIN check first, and would wrongly have reported the capability as having been used even when it was not). That fix was reverted in commit a70c7b3cbc06 ("tun: revert fix group permission check") due to allegedly causing a regression in an selinux test suite which *expected* the attachment to succeed when authorised by none of user, group, nor CAP_NET_ADMIN: https://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/ We should not break UAPI. But we don't have to consider an selinux test case which deliberately exercises a security flaw to be UAPI worth preserving either. To which end, I have fixed it in selinux-testsuite commit b2f894f0016b ("tests/tun_tap: set an owner on the device for the relabel tests"). So: fix the lack of CAP_NET_ADMIN check on devices which *haven't* been assigned an owner or group, while leaving the weird tun ownership model as it was (user *and* group have to match, if both are set). If someone still wants to fix the latter (which wasn't actually the reason the previous attempt was reverted), they can do it under separate cover. Permit attaching to an existing device only if an owner and/or group was set and the caller matches all that were set, or if the caller has CAP_NET_ADMIN. The only behavioural change is that a device with no owner or group now requires CAP_NET_ADMIN to attach — precisely the loophole we want to close. And put the CAP_NET_ADMIN check in the right place this time.

Severity

No CVSS data available.

Assigner

Linux CNA under the mitre root

CNA scorecard D 53/100 over 6651 records in the last 180 days details

References

3 references

URL	Tags
https://git.kernel.org/stable/c/2f92c0286cfd58bff…
https://git.kernel.org/stable/c/e53d1cf05da8ea58a…
https://git.kernel.org/stable/c/ffdf678dd16610e3f…

Impacted products

2 products

Vendor	Product	Version	CPE status
Linux	Linux	Affected: ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0 , < 2f92c0286cfd58bff9d6d54c01a771073d5eb775 (git) Affected: ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0 , < e53d1cf05da8ea58a5743b7ce5894fb51b0b9700 (git) Affected: ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0 , < ffdf678dd16610e3f006dac904bd37c09684673c (git)	guessed
Linux	Linux	Affected: 2.6.18 Unaffected: 0 , < 2.6.18 (semver) Unaffected: 6.18.61 , ≤ 6.18.* (semver) Unaffected: 7.3.2 , ≤ 7.3.* (semver) Unaffected: 7.4-rc1 , ≤ * (original_commit_for_fix)	guessed

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/tun.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "2f92c0286cfd58bff9d6d54c01a771073d5eb775",
              "status": "affected",
              "version": "ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0",
              "versionType": "git"
            },
            {
              "lessThan": "e53d1cf05da8ea58a5743b7ce5894fb51b0b9700",
              "status": "affected",
              "version": "ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0",
              "versionType": "git"
            },
            {
              "lessThan": "ffdf678dd16610e3f006dac904bd37c09684673c",
              "status": "affected",
              "version": "ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/tun.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.18"
            },
            {
              "lessThan": "2.6.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.61",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.3.*",
              "status": "unaffected",
              "version": "7.3.2",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.4-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.61",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3.2",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.4-rc1",
                  "versionStartIncluding": "2.6.18",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntun: Require CAP_NET_ADMIN to attach to an ownerless device\n\nTwenty years ago I made creating a tuntap device require CAP_NET_ADMIN\nin commit ca6bb5d7ab22 (\"[NET]: Require CAP_NET_ADMIN to create tuntap\ndevices.\")\n\nThe idea was to allow the permissions on /dev/net/tun to be relaxed to\n0666 and thus allow owners of tun devices assigned with TUNSETOWNER to\nactually open it and get at their devices.\n\nWhat we missed at the time was that persistent devices with *no* owner\nwere already essentially world-consumable, and anyone who could open\nthe device node could also attach to those.\n\nEven then, using persistent devices with no explicitly set owner \u2014 on\nthe (false) presumption that CAP_NET_ADMIN would be required to open\nthem \u2014 wasn\u0027t an egregious userspace bug. There are cases where it does\nmake sense to separate the creation/configuration of the netdevice, from\nthe process which shovels packets into it.\n\nSince then, TUNSETGROUP was added a year later in commit 8c644623fe7e\n(\"[NET]: Allow group ownership of TUN/TAP devices.\"). Its commit message\nnoted that if both uid and gid are set, both have to match (in itself a\nbizarre choice) \u2014 but still not that with *neither* set, no permission\nat all was required.\n\nThen in 2012 commit c8d68e6be1c3 (\"tuntap: multiqueue support\") allowed\nnew queues to be attached to a device from the moment of its creation,\nwith no way for userspace to close the race between creation and a\nsubsequent TUNSET{OWNER,GROUP}.\n\nIn 2024, commit 3ca459eaba1bf (\"tun: fix group permission check\") tried\nto fix things to be saner: only require the user *or* the group to\nmatch, in line with standard POSIX permissions, and require\nCAP_NET_ADMIN if neither the user nor group authorised the access\n(although it put the CAP_NET_ADMIN check first, and would wrongly have\nreported the capability as having been used even when it was not).\n\nThat fix was reverted in commit a70c7b3cbc06 (\"tun: revert fix group\npermission check\") due to allegedly causing a regression in an selinux\ntest suite which *expected* the attachment to succeed when authorised\nby none of user, group, nor CAP_NET_ADMIN:\nhttps://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/\n\nWe should not break UAPI. But we don\u0027t have to consider an selinux test\ncase which deliberately exercises a security flaw to be UAPI worth\npreserving either. To which end, I have fixed it in selinux-testsuite\ncommit b2f894f0016b (\"tests/tun_tap: set an owner on the device for the\nrelabel tests\").\n\nSo: fix the lack of CAP_NET_ADMIN check on devices which *haven\u0027t* been\nassigned an owner or group, while leaving the weird tun ownership model\nas it was (user *and* group have to match, if both are set). If someone\nstill wants to fix the latter (which wasn\u0027t actually the reason the\nprevious attempt was reverted), they can do it under separate cover.\n\nPermit attaching to an existing device only if an owner and/or group was\nset and the caller matches all that were set, or if the caller has\nCAP_NET_ADMIN. The only behavioural change is that a device with no\nowner or group now requires CAP_NET_ADMIN to attach \u2014 precisely the\nloophole we want to close.\n\nAnd put the CAP_NET_ADMIN check in the right place this time."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-11-07T14:08:47.735Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/2f92c0286cfd58bff9d6d54c01a771073d5eb775"
        },
        {
          "url": "https://git.kernel.org/stable/c/e53d1cf05da8ea58a5743b7ce5894fb51b0b9700"
        },
        {
          "url": "https://git.kernel.org/stable/c/ffdf678dd16610e3f006dac904bd37c09684673c"
        }
      ],
      "title": "tun: Require CAP_NET_ADMIN to attach to an ownerless device",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-99281",
    "datePublished": "2026-11-07T14:08:47.735Z",
    "dateReserved": "2026-09-25T10:25:14.405Z",
    "dateUpdated": "2026-11-07T14:08:47.735Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "drivers/net/tun.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
                  {
                    "lessThan": "2f92c0286cfd58bff9d6d54c01a771073d5eb775",
                    "status": "affected",
                    "version": "ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0",
                    "versionType": "git"
                  },
                  {
                    "lessThan": "e53d1cf05da8ea58a5743b7ce5894fb51b0b9700",
                    "status": "affected",
                    "version": "ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0",
                    "versionType": "git"
                  },
                  {
                    "lessThan": "ffdf678dd16610e3f006dac904bd37c09684673c",
                    "status": "affected",
                    "version": "ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0",
                    "versionType": "git"
                  }
                ]
              },
              {
                "defaultStatus": "affected",
                "product": "Linux",
                "programFiles": [
                  "drivers/net/tun.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
                  {
                    "status": "affected",
                    "version": "2.6.18"
                  },
                  {
                    "lessThan": "2.6.18",
                    "status": "unaffected",
                    "version": "0",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "6.18.*",
                    "status": "unaffected",
                    "version": "6.18.61",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "7.3.*",
                    "status": "unaffected",
                    "version": "7.3.2",
                    "versionType": "semver"
                  },
                  {
                    "lessThanOrEqual": "*",
                    "status": "unaffected",
                    "version": "7.4-rc1",
                    "versionType": "original_commit_for_fix"
                  }
                ]
              }
            ],
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntun: Require CAP_NET_ADMIN to attach to an ownerless device\n\nTwenty years ago I made creating a tuntap device require CAP_NET_ADMIN\nin commit ca6bb5d7ab22 (\"[NET]: Require CAP_NET_ADMIN to create tuntap\ndevices.\")\n\nThe idea was to allow the permissions on /dev/net/tun to be relaxed to\n0666 and thus allow owners of tun devices assigned with TUNSETOWNER to\nactually open it and get at their devices.\n\nWhat we missed at the time was that persistent devices with *no* owner\nwere already essentially world-consumable, and anyone who could open\nthe device node could also attach to those.\n\nEven then, using persistent devices with no explicitly set owner \u2014 on\nthe (false) presumption that CAP_NET_ADMIN would be required to open\nthem \u2014 wasn\u0027t an egregious userspace bug. There are cases where it does\nmake sense to separate the creation/configuration of the netdevice, from\nthe process which shovels packets into it.\n\nSince then, TUNSETGROUP was added a year later in commit 8c644623fe7e\n(\"[NET]: Allow group ownership of TUN/TAP devices.\"). Its commit message\nnoted that if both uid and gid are set, both have to match (in itself a\nbizarre choice) \u2014 but still not that with *neither* set, no permission\nat all was required.\n\nThen in 2012 commit c8d68e6be1c3 (\"tuntap: multiqueue support\") allowed\nnew queues to be attached to a device from the moment of its creation,\nwith no way for userspace to close the race between creation and a\nsubsequent TUNSET{OWNER,GROUP}.\n\nIn 2024, commit 3ca459eaba1bf (\"tun: fix group permission check\") tried\nto fix things to be saner: only require the user *or* the group to\nmatch, in line with standard POSIX permissions, and require\nCAP_NET_ADMIN if neither the user nor group authorised the access\n(although it put the CAP_NET_ADMIN check first, and would wrongly have\nreported the capability as having been used even when it was not).\n\nThat fix was reverted in commit a70c7b3cbc06 (\"tun: revert fix group\npermission check\") due to allegedly causing a regression in an selinux\ntest suite which *expected* the attachment to succeed when authorised\nby none of user, group, nor CAP_NET_ADMIN:\nhttps://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/\n\nWe should not break UAPI. But we don\u0027t have to consider an selinux test\ncase which deliberately exercises a security flaw to be UAPI worth\npreserving either. To which end, I have fixed it in selinux-testsuite\ncommit b2f894f0016b (\"tests/tun_tap: set an owner on the device for the\nrelabel tests\").\n\nSo: fix the lack of CAP_NET_ADMIN check on devices which *haven\u0027t* been\nassigned an owner or group, while leaving the weird tun ownership model\nas it was (user *and* group have to match, if both are set). If someone\nstill wants to fix the latter (which wasn\u0027t actually the reason the\nprevious attempt was reverted), they can do it under separate cover.\n\nPermit attaching to an existing device only if an owner and/or group was\nset and the caller matches all that were set, or if the caller has\nCAP_NET_ADMIN. The only behavioural change is that a device with no\nowner or group now requires CAP_NET_ADMIN to attach \u2014 precisely the\nloophole we want to close.\n\nAnd put the CAP_NET_ADMIN check in the right place this time."
          }
        ],
        "id": "CVE-2026-99281",
        "lastModified": "2026-11-07T14:17:03.790",
        "metrics": {},
        "published": "2026-11-07T14:17:03.790",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/2f92c0286cfd58bff9d6d54c01a771073d5eb775"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/e53d1cf05da8ea58a5743b7ce5894fb51b0b9700"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/ffdf678dd16610e3f006dac904bd37c09684673c"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    }
  }
}

FKIE_CVE-2026-99281

Vulnerability from fkie_nvd - Published: 2026-11-07 14:17 - Updated: 2026-11-07 14:17

Severity

Summary

References

	URL	Tags
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/2f92c0286cfd58bff9d6d54c01a771073d5eb775
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/e53d1cf05da8ea58a5743b7ce5894fb51b0b9700
	416baaa9-dc9f-4396-8d5f-8c081fb06d67	https://git.kernel.org/stable/c/ffdf678dd16610e3f006dac904bd37c09684673c

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/tun.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "2f92c0286cfd58bff9d6d54c01a771073d5eb775",
              "status": "affected",
              "version": "ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0",
              "versionType": "git"
            },
            {
              "lessThan": "e53d1cf05da8ea58a5743b7ce5894fb51b0b9700",
              "status": "affected",
              "version": "ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0",
              "versionType": "git"
            },
            {
              "lessThan": "ffdf678dd16610e3f006dac904bd37c09684673c",
              "status": "affected",
              "version": "ca6bb5d7ab22ac79f608fe6cbc6b12de6a5a19f0",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/tun.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.18"
            },
            {
              "lessThan": "2.6.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.61",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.3.*",
              "status": "unaffected",
              "version": "7.3.2",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.4-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntun: Require CAP_NET_ADMIN to attach to an ownerless device\n\nTwenty years ago I made creating a tuntap device require CAP_NET_ADMIN\nin commit ca6bb5d7ab22 (\"[NET]: Require CAP_NET_ADMIN to create tuntap\ndevices.\")\n\nThe idea was to allow the permissions on /dev/net/tun to be relaxed to\n0666 and thus allow owners of tun devices assigned with TUNSETOWNER to\nactually open it and get at their devices.\n\nWhat we missed at the time was that persistent devices with *no* owner\nwere already essentially world-consumable, and anyone who could open\nthe device node could also attach to those.\n\nEven then, using persistent devices with no explicitly set owner \u2014 on\nthe (false) presumption that CAP_NET_ADMIN would be required to open\nthem \u2014 wasn\u0027t an egregious userspace bug. There are cases where it does\nmake sense to separate the creation/configuration of the netdevice, from\nthe process which shovels packets into it.\n\nSince then, TUNSETGROUP was added a year later in commit 8c644623fe7e\n(\"[NET]: Allow group ownership of TUN/TAP devices.\"). Its commit message\nnoted that if both uid and gid are set, both have to match (in itself a\nbizarre choice) \u2014 but still not that with *neither* set, no permission\nat all was required.\n\nThen in 2012 commit c8d68e6be1c3 (\"tuntap: multiqueue support\") allowed\nnew queues to be attached to a device from the moment of its creation,\nwith no way for userspace to close the race between creation and a\nsubsequent TUNSET{OWNER,GROUP}.\n\nIn 2024, commit 3ca459eaba1bf (\"tun: fix group permission check\") tried\nto fix things to be saner: only require the user *or* the group to\nmatch, in line with standard POSIX permissions, and require\nCAP_NET_ADMIN if neither the user nor group authorised the access\n(although it put the CAP_NET_ADMIN check first, and would wrongly have\nreported the capability as having been used even when it was not).\n\nThat fix was reverted in commit a70c7b3cbc06 (\"tun: revert fix group\npermission check\") due to allegedly causing a regression in an selinux\ntest suite which *expected* the attachment to succeed when authorised\nby none of user, group, nor CAP_NET_ADMIN:\nhttps://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/\n\nWe should not break UAPI. But we don\u0027t have to consider an selinux test\ncase which deliberately exercises a security flaw to be UAPI worth\npreserving either. To which end, I have fixed it in selinux-testsuite\ncommit b2f894f0016b (\"tests/tun_tap: set an owner on the device for the\nrelabel tests\").\n\nSo: fix the lack of CAP_NET_ADMIN check on devices which *haven\u0027t* been\nassigned an owner or group, while leaving the weird tun ownership model\nas it was (user *and* group have to match, if both are set). If someone\nstill wants to fix the latter (which wasn\u0027t actually the reason the\nprevious attempt was reverted), they can do it under separate cover.\n\nPermit attaching to an existing device only if an owner and/or group was\nset and the caller matches all that were set, or if the caller has\nCAP_NET_ADMIN. The only behavioural change is that a device with no\nowner or group now requires CAP_NET_ADMIN to attach \u2014 precisely the\nloophole we want to close.\n\nAnd put the CAP_NET_ADMIN check in the right place this time."
    }
  ],
  "id": "CVE-2026-99281",
  "lastModified": "2026-11-07T14:17:03.790",
  "metrics": {},
  "published": "2026-11-07T14:17:03.790",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/2f92c0286cfd58bff9d6d54c01a771073d5eb775"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e53d1cf05da8ea58a5743b7ce5894fb51b0b9700"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ffdf678dd16610e3f006dac904bd37c09684673c"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}

GHSA-CFRF-W8R8-RF8X

Vulnerability from github – Published: 2026-11-07 15:30 – Updated: 2026-11-07 15:30

Details

In the Linux kernel, the following vulnerability has been resolved:

tun: Require CAP_NET_ADMIN to attach to an ownerless device

Twenty years ago I made creating a tuntap device require CAP_NET_ADMIN in commit ca6bb5d7ab22 ("[NET]: Require CAP_NET_ADMIN to create tuntap devices.")

The idea was to allow the permissions on /dev/net/tun to be relaxed to 0666 and thus allow owners of tun devices assigned with TUNSETOWNER to actually open it and get at their devices.

What we missed at the time was that persistent devices with no owner were already essentially world-consumable, and anyone who could open the device node could also attach to those.

Even then, using persistent devices with no explicitly set owner — on the (false) presumption that CAP_NET_ADMIN would be required to open them — wasn't an egregious userspace bug. There are cases where it does make sense to separate the creation/configuration of the netdevice, from the process which shovels packets into it.

Since then, TUNSETGROUP was added a year later in commit 8c644623fe7e ("[NET]: Allow group ownership of TUN/TAP devices."). Its commit message noted that if both uid and gid are set, both have to match (in itself a bizarre choice) — but still not that with neither set, no permission at all was required.

Then in 2012 commit c8d68e6be1c3 ("tuntap: multiqueue support") allowed new queues to be attached to a device from the moment of its creation, with no way for userspace to close the race between creation and a subsequent TUNSET{OWNER,GROUP}.

In 2024, commit 3ca459eaba1bf ("tun: fix group permission check") tried to fix things to be saner: only require the user or the group to match, in line with standard POSIX permissions, and require CAP_NET_ADMIN if neither the user nor group authorised the access (although it put the CAP_NET_ADMIN check first, and would wrongly have reported the capability as having been used even when it was not).

That fix was reverted in commit a70c7b3cbc06 ("tun: revert fix group permission check") due to allegedly causing a regression in an selinux test suite which expected the attachment to succeed when authorised by none of user, group, nor CAP_NET_ADMIN: https://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/

We should not break UAPI. But we don't have to consider an selinux test case which deliberately exercises a security flaw to be UAPI worth preserving either. To which end, I have fixed it in selinux-testsuite commit b2f894f0016b ("tests/tun_tap: set an owner on the device for the relabel tests").

So: fix the lack of CAP_NET_ADMIN check on devices which haven't been assigned an owner or group, while leaving the weird tun ownership model as it was (user and group have to match, if both are set). If someone still wants to fix the latter (which wasn't actually the reason the previous attempt was reverted), they can do it under separate cover.

Permit attaching to an existing device only if an owner and/or group was set and the caller matches all that were set, or if the caller has CAP_NET_ADMIN. The only behavioural change is that a device with no owner or group now requires CAP_NET_ADMIN to attach — precisely the loophole we want to close.

And put the CAP_NET_ADMIN check in the right place this time.

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-99281"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-11-07T14:17:03Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ntun: Require CAP_NET_ADMIN to attach to an ownerless device\n\nTwenty years ago I made creating a tuntap device require CAP_NET_ADMIN\nin commit ca6bb5d7ab22 (\"[NET]: Require CAP_NET_ADMIN to create tuntap\ndevices.\")\n\nThe idea was to allow the permissions on /dev/net/tun to be relaxed to\n0666 and thus allow owners of tun devices assigned with TUNSETOWNER to\nactually open it and get at their devices.\n\nWhat we missed at the time was that persistent devices with *no* owner\nwere already essentially world-consumable, and anyone who could open\nthe device node could also attach to those.\n\nEven then, using persistent devices with no explicitly set owner \u2014 on\nthe (false) presumption that CAP_NET_ADMIN would be required to open\nthem \u2014 wasn\u0027t an egregious userspace bug. There are cases where it does\nmake sense to separate the creation/configuration of the netdevice, from\nthe process which shovels packets into it.\n\nSince then, TUNSETGROUP was added a year later in commit 8c644623fe7e\n(\"[NET]: Allow group ownership of TUN/TAP devices.\"). Its commit message\nnoted that if both uid and gid are set, both have to match (in itself a\nbizarre choice) \u2014 but still not that with *neither* set, no permission\nat all was required.\n\nThen in 2012 commit c8d68e6be1c3 (\"tuntap: multiqueue support\") allowed\nnew queues to be attached to a device from the moment of its creation,\nwith no way for userspace to close the race between creation and a\nsubsequent TUNSET{OWNER,GROUP}.\n\nIn 2024, commit 3ca459eaba1bf (\"tun: fix group permission check\") tried\nto fix things to be saner: only require the user *or* the group to\nmatch, in line with standard POSIX permissions, and require\nCAP_NET_ADMIN if neither the user nor group authorised the access\n(although it put the CAP_NET_ADMIN check first, and would wrongly have\nreported the capability as having been used even when it was not).\n\nThat fix was reverted in commit a70c7b3cbc06 (\"tun: revert fix group\npermission check\") due to allegedly causing a regression in an selinux\ntest suite which *expected* the attachment to succeed when authorised\nby none of user, group, nor CAP_NET_ADMIN:\nhttps://lore.kernel.org/netdev/CAFqZXNtkCBT4f+PwyVRmQGoT3p1eVa01fCG_aNtpt6dakXncUg@mail.gmail.com/\n\nWe should not break UAPI. But we don\u0027t have to consider an selinux test\ncase which deliberately exercises a security flaw to be UAPI worth\npreserving either. To which end, I have fixed it in selinux-testsuite\ncommit b2f894f0016b (\"tests/tun_tap: set an owner on the device for the\nrelabel tests\").\n\nSo: fix the lack of CAP_NET_ADMIN check on devices which *haven\u0027t* been\nassigned an owner or group, while leaving the weird tun ownership model\nas it was (user *and* group have to match, if both are set). If someone\nstill wants to fix the latter (which wasn\u0027t actually the reason the\nprevious attempt was reverted), they can do it under separate cover.\n\nPermit attaching to an existing device only if an owner and/or group was\nset and the caller matches all that were set, or if the caller has\nCAP_NET_ADMIN. The only behavioural change is that a device with no\nowner or group now requires CAP_NET_ADMIN to attach \u2014 precisely the\nloophole we want to close.\n\nAnd put the CAP_NET_ADMIN check in the right place this time.",
  "id": "GHSA-cfrf-w8r8-rf8x",
  "modified": "2026-11-07T15:30:29Z",
  "published": "2026-11-07T15:30:28Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99281"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2f92c0286cfd58bff9d6d54c01a771073d5eb775"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e53d1cf05da8ea58a5743b7ce5894fb51b0b9700"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ffdf678dd16610e3f006dac904bd37c09684673c"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

Order JSON

How durations are calculated

Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

Publication & reservation Sightings KEV catalogs Other timestamps

Loading timeline…

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-99281 (GCVE-0-2026-99281)

FKIE_CVE-2026-99281

GHSA-CFRF-W8R8-RF8X

Tags

Sightings

Nomenclature

Vulnerability timeline

Related by attack behaviour