FKIE_CVE-2026-74658

Vulnerability from fkie_nvd - Published: 2026-08-22 16:16 - Updated: 2026-08-22 16:16
Severity
Summary
In the Linux kernel, the following vulnerability has been resolved: futex: Prevent robust futex exit race some more A robust futex unlock stores 0 over the whole futex value - wiping FUTEX_WAITERS - and wakes a single waiter. That wakeup is a one-shot notification: the protocol relies on its recipient to either acquire the futex (and eventually unlock while aware of the remaining contention) or re-arm FUTEX_WAITERS before sleeping again. If the woken waiter is killed before it can do either, the kernel must jump in and wake the next task down the line. This is a known complication of the futex protocol with a previous partial fix in commit ca16d5bee598 ("futex: Prevent robust futex exit race"). Unfortunately, that fix is insufficient. If a third task re-acquired the futex through the uncontended fast path in the meantime, the notification is lost: robust exit processing sees that it is owned by another task and does nothing, while the new owner sees no FUTEX_WAITERS when it unlocks and wakes nobody. The remaining waiters sleep forever behind a free futex: A owns the futex, B and C sleep in FUTEX_WAIT uval == A | FUTEX_WAITERS A robust unlock: store 0, FUTEX_WAKE(1) wakes B uval == 0 D fast path acquire: cmpxchg(0 -> D) uval == D, no FUTEX_WAITERS B killed before acting on the wakeup B exit walk, pending op: owner D != B -> no action D unlock: no FUTEX_WAITERS -> no wake C sleeps forever This is clearly a shortcoming in the implementation, which fails to keep the FUTEX_WAITERS bit consistent. Work around this by augmenting the robust list exit processing to also perform the extra wakeup if the futex word is owned by another thread but FUTEX_WAITERS is not set. This does not fix the problem of a non-contended take over/release and free sequence, which has been discussed for years and has been addressed by commit 3ca9595d9fb6 ("futex: Add support for unlocking robust futexes") and subsequent changes, but failed to take the problem described above into account. A more complete solution which is based on the in kernel unlock of contended robust futexes has been discussed in the context of this change and should show up in mainline sooner than later. [ tglx: Amend change log slightly and fixup coding style ]
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/33bfa85458105d6169ebdb697f692b8bb8025bae
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/6d4514ca9cdf61fec4ec634cf50386f6f7e69748
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7b8c53263f8878bdd12c87e147ac6feca5c05211
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7cf710e70f9bb8ea75f759ebed09871801315992
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/83b0f71d5a313a765754acab51d2ecc5de76e0b9
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/925628656b73b70930972ccde421de4f758d8650
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a1c2b7b86a946b6b172bce44d74553da2323a36c
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/aa5c571901c6b22b58373693a4bf889ecab11ff5
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/futex/core.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "83b0f71d5a313a765754acab51d2ecc5de76e0b9",
              "status": "affected",
              "version": "ca16d5bee59807bf04deaab0a8eccecd5061528c",
              "versionType": "git"
            },
            {
              "lessThan": "a1c2b7b86a946b6b172bce44d74553da2323a36c",
              "status": "affected",
              "version": "ca16d5bee59807bf04deaab0a8eccecd5061528c",
              "versionType": "git"
            },
            {
              "lessThan": "33bfa85458105d6169ebdb697f692b8bb8025bae",
              "status": "affected",
              "version": "ca16d5bee59807bf04deaab0a8eccecd5061528c",
              "versionType": "git"
            },
            {
              "lessThan": "aa5c571901c6b22b58373693a4bf889ecab11ff5",
              "status": "affected",
              "version": "ca16d5bee59807bf04deaab0a8eccecd5061528c",
              "versionType": "git"
            },
            {
              "lessThan": "925628656b73b70930972ccde421de4f758d8650",
              "status": "affected",
              "version": "ca16d5bee59807bf04deaab0a8eccecd5061528c",
              "versionType": "git"
            },
            {
              "lessThan": "7b8c53263f8878bdd12c87e147ac6feca5c05211",
              "status": "affected",
              "version": "ca16d5bee59807bf04deaab0a8eccecd5061528c",
              "versionType": "git"
            },
            {
              "lessThan": "7cf710e70f9bb8ea75f759ebed09871801315992",
              "status": "affected",
              "version": "ca16d5bee59807bf04deaab0a8eccecd5061528c",
              "versionType": "git"
            },
            {
              "lessThan": "6d4514ca9cdf61fec4ec634cf50386f6f7e69748",
              "status": "affected",
              "version": "ca16d5bee59807bf04deaab0a8eccecd5061528c",
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            },
            {
              "status": "affected",
              "version": "8dd558881e0f4d6942c19bd8f7b1a7c19becb59e",
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            },
            {
              "status": "affected",
              "version": "b90aa237f469c3575190a5e6a855b76ad1d2ce94",
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            },
            {
              "status": "affected",
              "version": "3e24098da750991f75819069c79e090dfd029219",
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            },
            {
              "status": "affected",
              "version": "2819f4030f43057238992a4adcd950d7c95aff65",
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            },
            {
              "status": "affected",
              "version": "2c60b44d8ba9d62c2693d2692f118177f212b1a8",
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            },
            {
              "status": "affected",
              "version": "82ca3ab31b9cf23b86436a85381e4c5757bc6b80",
              "versionType": "git"
            },
            {
              "lessThan": "3.17",
              "status": "affected",
              "version": "3.16.82",
              "versionType": "semver"
            },
            {
              "lessThan": "4.10",
              "status": "affected",
              "version": "4.9.264",
              "versionType": "semver"
            },
            {
              "lessThan": "4.15",
              "status": "affected",
              "version": "4.14.158",
              "versionType": "semver"
            },
            {
              "lessThan": "4.20",
              "status": "affected",
              "version": "4.19.87",
              "versionType": "semver"
            },
            {
              "lessThan": "5.4",
              "status": "affected",
              "version": "5.3.14",
              "versionType": "semver"
            },
            {
              "lessThan": "5.5",
              "status": "affected",
              "version": "5.4.1",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "kernel/futex/core.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.5"
            },
            {
              "lessThan": "5.5",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.265",
              "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": "6.6.152",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.104",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.45",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.9",
              "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\nfutex: Prevent robust futex exit race some more\n\nA robust futex unlock stores 0 over the whole futex value - wiping\nFUTEX_WAITERS - and wakes a single waiter. That wakeup is a one-shot\nnotification: the protocol relies on its recipient to either acquire the\nfutex (and eventually unlock while aware of the remaining contention) or\nre-arm FUTEX_WAITERS before sleeping again.  If the woken waiter is killed\nbefore it can do either, the kernel must jump in and wake the next task\ndown the line.\n\nThis is a known complication of the futex protocol with a previous\npartial fix in commit ca16d5bee598 (\"futex: Prevent robust futex exit\nrace\"). Unfortunately, that fix is insufficient.\n\nIf a third task re-acquired the futex through the uncontended fast\npath in the meantime, the notification is lost: robust exit processing\nsees that it is owned by another task and does nothing, while the new\nowner sees no FUTEX_WAITERS when it unlocks and wakes nobody.\nThe remaining waiters sleep forever behind a free futex:\n\n  A owns the futex, B and C sleep in FUTEX_WAIT\n                                        uval == A | FUTEX_WAITERS\n  A robust unlock: store 0, FUTEX_WAKE(1) wakes B\n                                        uval == 0\n  D fast path acquire: cmpxchg(0 -\u003e D)\n                                        uval == D, no FUTEX_WAITERS\n  B killed before acting on the wakeup\n  B exit walk, pending op: owner D != B -\u003e no action\n  D unlock: no FUTEX_WAITERS -\u003e no wake\n                                        C sleeps forever\n\nThis is clearly a shortcoming in the implementation, which fails to keep\nthe FUTEX_WAITERS bit consistent.\n\nWork around this by augmenting the robust list exit processing to also\nperform the extra wakeup if the futex word is owned by another thread but\nFUTEX_WAITERS is not set.\n\nThis does not fix the problem of a non-contended take over/release and free\nsequence, which has been discussed for years and has been addressed by\ncommit 3ca9595d9fb6 (\"futex: Add support for unlocking robust futexes\") and\nsubsequent changes, but failed to take the problem described above into\naccount.\n\nA more complete solution which is based on the in kernel unlock of\ncontended robust futexes has been discussed in the context of this change\nand should show up in mainline sooner than later.\n\n[ tglx: Amend change log slightly and fixup coding style ]"
    }
  ],
  "id": "CVE-2026-74658",
  "lastModified": "2026-08-22T16:16:39.453",
  "metrics": {},
  "published": "2026-08-22T16:16:39.453",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/33bfa85458105d6169ebdb697f692b8bb8025bae"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/6d4514ca9cdf61fec4ec634cf50386f6f7e69748"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/7b8c53263f8878bdd12c87e147ac6feca5c05211"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/7cf710e70f9bb8ea75f759ebed09871801315992"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/83b0f71d5a313a765754acab51d2ecc5de76e0b9"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/925628656b73b70930972ccde421de4f758d8650"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/a1c2b7b86a946b6b172bce44d74553da2323a36c"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/aa5c571901c6b22b58373693a4bf889ecab11ff5"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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