FKIE_CVE-2026-68398

Vulnerability from fkie_nvd - Published: 2026-08-10 13:20 - Updated: 2026-08-19 17:20
Severity
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF pppol2tp_recv() runs in the L2TP UDP-encap softirq RX path: l2tp_udp_encap_recv() -> l2tp_recv_common() -> pppol2tp_recv() -> ppp_input(&po->chan) It runs under rcu_read_lock() holding only an l2tp_session reference and takes NO reference on the internal PPP channel (struct channel, chan->ppp) that ppp_input() dereferences. The pppox socket is SOCK_RCU_FREE, so 'po' and the embedded ppp_channel are RCU-safe. But the internal struct channel is a separate allocation that ppp_release_channel() frees with a plain kfree(): close(data socket) -> pppol2tp_release() -> pppox_unbind_sock() -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch) For a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit (no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips both ppp_disconnect_channel()'s synchronize_net() and ppp_unbridge_channels()'s synchronize_rcu(), so the kfree() has no grace period. rcu_read_lock() in pppol2tp_recv() does not protect against a plain kfree(), so an in-flight ppp_input() on one CPU can dereference the channel just freed by close() on another CPU. The bug is reachable by an unprivileged user. Defer the channel free to an RCU callback via call_rcu() so the grace period fences any in-flight ppp_input(). The disconnect and unbridge teardown paths already fence with synchronize_net()/synchronize_rcu(); call_rcu() does the same here without stalling the close() path.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/110b765744b147c63882f5e9cb12931c5dc8d85f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/4e47f1ac188ece11d6fdabe44166a2776cc5bd4e
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ec4215683e47424c9c4762fd3c60f552a3119142
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/ppp/ppp_generic.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "4e47f1ac188ece11d6fdabe44166a2776cc5bd4e",
              "status": "affected",
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "versionType": "git"
            },
            {
              "lessThan": "110b765744b147c63882f5e9cb12931c5dc8d85f",
              "status": "affected",
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "versionType": "git"
            },
            {
              "lessThan": "4bb84e964ff0fe0a171c965362de72f9820dbce9",
              "status": "affected",
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "versionType": "git"
            },
            {
              "lessThan": "3ab32218d7182705dae5c86f13925f458072da2c",
              "status": "affected",
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "versionType": "git"
            },
            {
              "lessThan": "c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa",
              "status": "affected",
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "versionType": "git"
            },
            {
              "lessThan": "06213c85d8c0994f786c093b8b2a517987943ca6",
              "status": "affected",
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "versionType": "git"
            },
            {
              "lessThan": "ec4215683e47424c9c4762fd3c60f552a3119142",
              "status": "affected",
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "d36e5ba7bbed5d7bd26e8609ffed503c2def401b",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "9bcc0508576b2d50efd958f2ea1c5906749c2c89",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "c2984681fe15cfb803a9132aaaf1140ab20a72c1",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "5803ecd7f6ac6f747582e775caa62ac9d0489261",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "26f8819ddd10141ebe7bbce700fbab36bfa5f478",
              "versionType": "git"
            },
            {
              "lessThan": "3.3",
              "status": "affected",
              "version": "3.2.99",
              "versionType": "semver"
            },
            {
              "lessThan": "3.17",
              "status": "affected",
              "version": "3.16.54",
              "versionType": "semver"
            },
            {
              "lessThan": "4.5",
              "status": "affected",
              "version": "4.4.225",
              "versionType": "semver"
            },
            {
              "lessThan": "4.10",
              "status": "affected",
              "version": "4.9.225",
              "versionType": "semver"
            },
            {
              "lessThan": "4.15",
              "status": "affected",
              "version": "4.14.182",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "drivers/net/ppp/ppp_generic.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.15"
            },
            {
              "lessThan": "4.15",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.216",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.183",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.148",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.101",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.42",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.6",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "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\nppp: defer channel free to an RCU grace period to fix pppol2tp RX UAF\n\npppol2tp_recv() runs in the L2TP UDP-encap softirq RX path:\n\n l2tp_udp_encap_recv() -\u003e l2tp_recv_common() -\u003e pppol2tp_recv()\n   -\u003e ppp_input(\u0026po-\u003echan)\n\nIt runs under rcu_read_lock() holding only an l2tp_session reference and\ntakes NO reference on the internal PPP channel (struct channel,\nchan-\u003eppp) that ppp_input() dereferences.\n\nThe pppox socket is SOCK_RCU_FREE, so \u0027po\u0027 and the embedded ppp_channel\nare RCU-safe.  But the internal struct channel is a separate allocation\nthat ppp_release_channel() frees with a plain kfree():\n\n close(data socket) -\u003e pppol2tp_release() -\u003e pppox_unbind_sock()\n   -\u003e ppp_unregister_channel() -\u003e ppp_release_channel() -\u003e kfree(pch)\n\nFor a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit\n(no PPPIOCCONNECT, pch-\u003eppp == NULL) and not bridged, teardown skips\nboth ppp_disconnect_channel()\u0027s synchronize_net() and\nppp_unbridge_channels()\u0027s synchronize_rcu(), so the kfree() has no grace\nperiod.  rcu_read_lock() in pppol2tp_recv() does not protect against a\nplain kfree(), so an in-flight ppp_input() on one CPU can dereference\nthe channel just freed by close() on another CPU.\n\nThe bug is reachable by an unprivileged user.\n\nDefer the channel free to an RCU callback via call_rcu() so the grace\nperiod fences any in-flight ppp_input(). The disconnect and unbridge\nteardown paths already fence with synchronize_net()/synchronize_rcu();\ncall_rcu() does the same here without stalling the close() path."
    }
  ],
  "id": "CVE-2026-68398",
  "lastModified": "2026-08-19T17:20:47.860",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.9,
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-08-10T13:20:33.243",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/110b765744b147c63882f5e9cb12931c5dc8d85f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/3ab32218d7182705dae5c86f13925f458072da2c"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/4bb84e964ff0fe0a171c965362de72f9820dbce9"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/4e47f1ac188ece11d6fdabe44166a2776cc5bd4e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ec4215683e47424c9c4762fd3c60f552a3119142"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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