Vulnerability-Lookup

GHSA-4VM9-M655-VQF4

Vulnerability from github – Published: 2026-06-09 15:32 – Updated: 2026-06-09 15:32

Details

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

9p: fix access mode flags being ORed instead of replaced

Since commit 1f3e4142c0eb ("9p: convert to the new mount API"), v9fs_apply_options() applies parsed mount flags with |= onto flags already set by v9fs_session_init(). For 9P2000.L, session_init sets V9FS_ACCESS_CLIENT as the default, so when the user mounts with "access=user", both bits end up set. Access mode checks compare against exact values, so having both bits set matches neither mode.

This causes v9fs_fid_lookup() to fall through to the default switch case, using INVALID_UID (nobody/65534) instead of current_fsuid() for all fid lookups. Root is then unable to chown or perform other privileged operations.

Fix by clearing the access mask before applying the user's choice.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-52906"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-06-09T14:16:45Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\n9p: fix access mode flags being ORed instead of replaced\n\nSince commit 1f3e4142c0eb (\"9p: convert to the new mount API\"),\nv9fs_apply_options() applies parsed mount flags with |= onto flags\nalready set by v9fs_session_init(). For 9P2000.L, session_init sets\nV9FS_ACCESS_CLIENT as the default, so when the user mounts with\n\"access=user\", both bits end up set. Access mode checks compare\nagainst exact values, so having both bits set matches neither mode.\n\nThis causes v9fs_fid_lookup() to fall through to the default switch\ncase, using INVALID_UID (nobody/65534) instead of current_fsuid()\nfor all fid lookups. Root is then unable to chown or perform other\nprivileged operations.\n\nFix by clearing the access mask before applying the user\u0027s choice.",
  "id": "GHSA-4vm9-m655-vqf4",
  "modified": "2026-06-09T15:32:19Z",
  "published": "2026-06-09T15:32:19Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-52906"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b8f037e87a083291190204b959cda417aaf01058"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-52906 (GCVE-0-2026-52906)

Vulnerability from cvelistv5 – Published: 2026-06-09 12:36 – Updated: 2026-06-09 12:36

Title

9p: fix access mode flags being ORed instead of replaced

Summary

In the Linux kernel, the following vulnerability has been resolved: 9p: fix access mode flags being ORed instead of replaced Since commit 1f3e4142c0eb ("9p: convert to the new mount API"), v9fs_apply_options() applies parsed mount flags with |= onto flags already set by v9fs_session_init(). For 9P2000.L, session_init sets V9FS_ACCESS_CLIENT as the default, so when the user mounts with "access=user", both bits end up set. Access mode checks compare against exact values, so having both bits set matches neither mode. This causes v9fs_fid_lookup() to fall through to the default switch case, using INVALID_UID (nobody/65534) instead of current_fsuid() for all fid lookups. Root is then unable to chown or perform other privileged operations. Fix by clearing the access mask before applying the user's choice.

Severity

No CVSS data available.

Assigner

Linux

References

2 references

URL	Tags
https://git.kernel.org/stable/c/b8f037e87a0832911…
https://git.kernel.org/stable/c/da2346a48a5a1fed8…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 1f3e4142c0eb178089ea0cbc97506a061470ad27 , < b8f037e87a083291190204b959cda417aaf01058 (git) Affected: 1f3e4142c0eb178089ea0cbc97506a061470ad27 , < da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9 (git)
Linux	Linux	Affected: 6.19 Unaffected: 0 , < 6.19 (semver) Unaffected: 7.0.4 , ≤ 7.0.* (semver) Unaffected: 7.1-rc1 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/9p/v9fs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "b8f037e87a083291190204b959cda417aaf01058",
              "status": "affected",
              "version": "1f3e4142c0eb178089ea0cbc97506a061470ad27",
              "versionType": "git"
            },
            {
              "lessThan": "da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9",
              "status": "affected",
              "version": "1f3e4142c0eb178089ea0cbc97506a061470ad27",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/9p/v9fs.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "lessThan": "6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.0.*",
              "status": "unaffected",
              "version": "7.0.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.0.4",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1-rc1",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\n9p: fix access mode flags being ORed instead of replaced\n\nSince commit 1f3e4142c0eb (\"9p: convert to the new mount API\"),\nv9fs_apply_options() applies parsed mount flags with |= onto flags\nalready set by v9fs_session_init(). For 9P2000.L, session_init sets\nV9FS_ACCESS_CLIENT as the default, so when the user mounts with\n\"access=user\", both bits end up set. Access mode checks compare\nagainst exact values, so having both bits set matches neither mode.\n\nThis causes v9fs_fid_lookup() to fall through to the default switch\ncase, using INVALID_UID (nobody/65534) instead of current_fsuid()\nfor all fid lookups. Root is then unable to chown or perform other\nprivileged operations.\n\nFix by clearing the access mask before applying the user\u0027s choice."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-09T12:36:03.521Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/b8f037e87a083291190204b959cda417aaf01058"
        },
        {
          "url": "https://git.kernel.org/stable/c/da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9"
        }
      ],
      "title": "9p: fix access mode flags being ORed instead of replaced",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-52906",
    "datePublished": "2026-06-09T12:36:03.521Z",
    "dateReserved": "2026-06-09T07:44:35.366Z",
    "dateUpdated": "2026-06-09T12:36:03.521Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-4VM9-M655-VQF4

CVE-2026-52906 (GCVE-0-2026-52906)

Tags

Sightings

Nomenclature