CVE-2026-68398

Full vulnerability record from the local CVENow database.

Description

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.

Severity

HIGH

CVSS score

7.8 (v3.1)

Vulnerability status

Received

Source identifier

416baaa9-dc9f-4396-8d5f-8c081fb06d67

Published

2026-08-10 13:20:33.243000

Last modified

2026-10-19 22:17:17.243000

View original CVE JSON

{
  "id": "CVE-2026-68398",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2026-08-10T13:20:33.243",
  "lastModified": "2026-10-19T22:17:17.243",
  "vulnStatus": "Received",
  "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() -> l2tp_recv_common() -> pppol2tp_recv()\n   -> ppp_input(&po->chan)\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->ppp) that ppp_input() dereferences.\n\nThe pppox socket is SOCK_RCU_FREE, so 'po' 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) -> pppol2tp_release() -> pppox_unbind_sock()\n   -> ppp_unregister_channel() -> ppp_release_channel() -> kfree(pch)\n\nFor a channel that is bound (PPPIOCGCHAN) but not attached to a ppp unit\n(no PPPIOCCONNECT, pch->ppp == NULL) and not bridged, teardown skips\nboth ppp_disconnect_channel()'s synchronize_net() and\nppp_unbridge_channels()'s 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."
    }
  ],
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "programFiles": [
            "drivers/net/ppp/ppp_generic.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "lessThan": "4e47f1ac188ece11d6fdabe44166a2776cc5bd4e",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "lessThan": "110b765744b147c63882f5e9cb12931c5dc8d85f",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "lessThan": "4bb84e964ff0fe0a171c965362de72f9820dbce9",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "lessThan": "3ab32218d7182705dae5c86f13925f458072da2c",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "lessThan": "c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "lessThan": "06213c85d8c0994f786c093b8b2a517987943ca6",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "ee40fb2e1eb5bc0ddd3f2f83c6e39a454ef5a741",
              "lessThan": "ec4215683e47424c9c4762fd3c60f552a3119142",
              "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",
              "status": "affected"
            },
            {
              "version": "3.2.99",
              "lessThan": "3.3",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "3.16.54",
              "lessThan": "3.17",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "4.4.225",
              "lessThan": "4.5",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "4.9.225",
              "lessThan": "4.10",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "4.14.182",
              "lessThan": "4.15",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "affected",
          "programFiles": [
            "drivers/net/ppp/ppp_generic.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "4.15",
              "status": "affected"
            },
            {
              "version": "0",
              "lessThan": "4.15",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "5.15.216",
              "lessThanOrEqual": "5.15.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.1.183",
              "lessThanOrEqual": "6.1.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.6.148",
              "lessThanOrEqual": "6.6.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.12.101",
              "lessThanOrEqual": "6.12.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.18.42",
              "lessThanOrEqual": "6.18.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.1.6",
              "lessThanOrEqual": "7.1.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.2",
              "lessThanOrEqual": "*",
              "versionType": "original_commit_for_fix",
              "status": "unaffected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "baseScore": 7.8,
          "baseSeverity": "HIGH",
          "attackVector": "LOCAL",
          "attackComplexity": "LOW",
          "privilegesRequired": "LOW",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.9
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-10-16T15:48:09.975001Z",
          "id": "CVE-2026-68398",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-416"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/06213c85d8c0994f786c093b8b2a517987943ca6",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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      "url": "https://git.kernel.org/stable/c/c9574b8a8edeb4edd3ac6472c27ef7184bdb2baa",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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    {
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
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}