{"id":"CVE-2026-89762","title":"apparmor: fix cred UAF caused by begin_current_label_crit_section()","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\napparmor: fix cred UAF caused by begin_current_label_crit_section()\n\nAppArmor's begin_current_label_crit_section() is a scary function called\nfrom lots of LSM hooks (in…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","cwe":["CWE-825"],"vendor":"Linux","product":"Linux","affected":["Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 089f10b47843a86fa03a8c20799c9353660e5288","Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 361488984d668235438faac28635f3632351407f","Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 587a6a92b93ec314c583bbf747413af170d42540","Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 580f777d6d9fd07fc034bd1aeba5c30fd48871a2","Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 3f4ae5fab613dca01d6a2a8210dd832e009fcf47","Linux 2.6.36"],"published":"2026-09-11","updated":"2026-10-21","sourceUpdated":"2026-10-21T12:48:39.169Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-89762","references":[{"url":"https://git.kernel.org/stable/c/089f10b47843a86fa03a8c20799c9353660e5288"},{"url":"https://git.kernel.org/stable/c/361488984d668235438faac28635f3632351407f"},{"url":"https://git.kernel.org/stable/c/587a6a92b93ec314c583bbf747413af170d42540"},{"url":"https://git.kernel.org/stable/c/580f777d6d9fd07fc034bd1aeba5c30fd48871a2"},{"url":"https://git.kernel.org/stable/c/3f4ae5fab613dca01d6a2a8210dd832e009fcf47"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89762.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-89762"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2532435"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89762"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89762"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89762.mbox"}],"tags":["cve.org","csaf","vex","red-hat","score-dispute"],"epss":0.00123,"epssPercentile":0.02047,"scores":{"cna":7.8,"vendor":5.5},"ingestedAt":"2026-09-14T15:23:07.472Z","slug":"CVE-2026-89762","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\napparmor: fix cred UAF caused by begin_current_label_crit_section()\n\nAppArmor's begin_current_label_crit_section() is a scary function called\nfrom lots of LSM hooks (in particular VFS/socket-related ones) that checks\nif the label referenced by the current creds is marked FLAG_STALE, and if\nso, attempts to use aa_replace_current_label() to replace the creds with an\nupdated version that uses a new label.\n\nThe first problem with this is that it would directly lead to UAF of\n`struct cred` if anything in the kernel takes a pointer to the current\ncreds and accesses these past a security hook invocation that replaces\ncreds, like so:\n```\nconst struct cred *cred = current_cred();\nalloc_file_pseudo(...);\nuid_t uid = cred->euid;\n```\nI don't know if anything in the kernel actually does this, but I think it\nis very surprising that this pattern could lead to UAF.\n\nThe second problem is that things go wrong when aa_replace_current_label()\nruns with overridden credentials. aa_replace_current_label() bails out if\n`current_cred() != current_real_cred()` (mirroring the check in\nproc_pid_attr_write()), but this check can't actually reliably detect\noverridden credentials because the overridden creds can be the same as the\nobjective creds.\n\nSo in approximately the following scenario, things go wrong:\n\n1. task begins with <creds A> (as both objective and subjective creds),\n   with refcount=2\n2. task grabs an extra reference on <creds A> for overriding\n3. task calls override_creds(<creds A>), which returns a pointer to the old\n   subjective creds (<creds A>)\n4. task enters AppArmor LSM hook\n5. AppArmor checks that objective/subjective creds are equal\n6. AppArmor replaces both cred pointers with <creds B> and drops 2 refs on\n   <creds A>\n7. task leaves AppArmor LSM hook\n8. task calls revert_creds(<creds A>)\n9. now task->cred is <creds A> while task->real_cred is <creds B>, but the\n   task_struct logically holds two references to <creds B>\n10. another task drops the extra reference on <creds A> that was used for\n    overriding, refcount drops to 0\n11. now task->real_cred points to freed creds\n\nAt this point, any access to current_cred() will be UAF.\n\nI have a test case where I run aa-disable on a profile while a process\nusing that profile is blocked on splice() from a FUSE passthrough file into\na full pipe; after the profile update, the pipe becomes empty, splice()\nresumes, the credentials go out of sync, and a subsequent getuid() syscall\nresults in a KASAN UAF splat.\n\nTo fix this, instead of directly replacing creds, do it via task_work that\nwill run at the end of the current syscall. (The point in time at which the\ncred replacement happens should have no correctness impact; it is just a\nperformance optimization to avoid unnecessarily touching the refcount of\nthe new label.)\n\nNote that AppArmor still performs direct cred replacements in the\nsb_pivotroot LSM hook after this change, and that direct cred replacements\ncan still happen in VFS ->write() callbacks via proc_pid_attr_write().\n\nThere are two options for what to do with aa_dup_task_ctx(): Either\nexplicitly reset new->label_replacement_pending after the entire\naa_task_ctx has been copied, or switch to manually copying members over.\nI am switching to manually copying members over because that should make\nbugs more obvious.\n\n## Affected\n\n- `Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 089f10b47843a86fa03a8c20799c9353660e5288`\n- `Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 361488984d668235438faac28635f3632351407f`\n- `Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 587a6a92b93ec314c583bbf747413af170d42540`\n- `Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 580f777d6d9fd07fc034bd1aeba5c30fd48871a2`\n- `Linux >= c75afcd153f6147d3b094f45a1d87e5df7f4f053 < 3f4ae5fab613dca01d6a2a8210dd832e009fcf47`\n- `Linux 2.6.36`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · updated 2026-09-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89762.json)","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":224566,"id":"CVE-2026-89762","ts":1792401411763,"field":"cvss","old":"5.5","new":"7.8"},{"seq":224565,"id":"CVE-2026-89762","ts":1792401411763,"field":"severity","old":"medium","new":"high"},{"seq":203897,"id":"CVE-2026-89762","ts":1789490215404,"field":"cvss","old":"5.2","new":"5.5"},{"seq":202954,"id":"CVE-2026-89762","ts":1789403733098,"field":"cvss","old":"7.8","new":"5.2"},{"seq":202953,"id":"CVE-2026-89762","ts":1789403733098,"field":"severity","old":"high","new":"medium"},{"seq":197666,"id":"CVE-2026-89762","ts":1789384318313,"field":"cvss","old":"5.2","new":"7.8"},{"seq":197665,"id":"CVE-2026-89762","ts":1789384318313,"field":"severity","old":"medium","new":"high"},{"seq":183641,"id":"CVE-2026-89762","ts":1789356676223,"field":"cvss","old":"7.8","new":"5.2"},{"seq":183640,"id":"CVE-2026-89762","ts":1789356676223,"field":"severity","old":"high","new":"medium"},{"seq":153650,"id":"CVE-2026-89762","ts":1789285351723,"field":"cvss","old":null,"new":"7.8"},{"seq":153649,"id":"CVE-2026-89762","ts":1789285351723,"field":"severity","old":"none","new":"high"},{"seq":147209,"id":"CVE-2026-89762","ts":1789270201404,"field":"cvss","old":null,"new":"5.2"},{"seq":147208,"id":"CVE-2026-89762","ts":1789270201404,"field":"severity","old":"none","new":"medium"},{"seq":108960,"id":"CVE-2026-89762","ts":1789183729743,"field":"cvss","old":null,"new":"5.2"},{"seq":108959,"id":"CVE-2026-89762","ts":1789183729743,"field":"severity","old":"none","new":"medium"}]}