{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89762", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.764Z", "datePublished": "2026-09-11T19:47:03.601Z", "dateUpdated": "2026-10-19T08:52:15.761Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:52:15.761Z" }, "descriptions": [ { "lang": "en", "value": "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 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 (as both objective and subjective creds),\n with refcount=2\n2. task grabs an extra reference on for overriding\n3. task calls override_creds(), which returns a pointer to the old\n subjective creds ()\n4. task enters AppArmor LSM hook\n5. AppArmor checks that objective/subjective creds are equal\n6. AppArmor replaces both cred pointers with and drops 2 refs on\n \n7. task leaves AppArmor LSM hook\n8. task calls revert_creds()\n9. now task->cred is while task->real_cred is , but the\n task_struct logically holds two references to \n10. another task drops the extra reference on 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." } ], "metrics": [ { "cvssV3_1": { "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" }, "scenarios": [ { "lang": "en", "value": "AV:L - begin_current_label_crit_section() runs from AppArmor LSM hooks on local VFS/socket syscalls after a stale profile replace. The confirmed UAF is splice from a FUSE passthrough file under override_creds() of the same cred object; unprivileged binfmt_misc register does the same around open_exec(). This is not a network receive path.\nAC:L - The attacker controls both sides: they replace the AppArmor profile to mark the task label FLAG_STALE, then invoke a syscall that override_creds()s with that same cred object (FUSE passthrough splice into a full pipe, or binfmt_misc OPEN_FILE register). The author’s sequence is attacker-driven, not a victim-dependent race.\nPR:L - Making the label stale requires AppArmor policy replace (CAP_MAC_ADMIN), but unprivileged_userns_apparmor_policy defaults to 1 so userns root can load/replace policy. The LSM hooks and same-cred override_creds sites, including unprivileged binfmt_misc (FS_USERNS_MOUNT), are reachable without init-namespace root.\nUI:N - The attacker confines their own task, replaces their own policy, and triggers the override_creds VFS path themselves; no separate victim user action is required.\nS:U - Impact is a kernel struct cred use-after-free and local privilege escalation within the same kernel security authority. It is not a VM escape, IOMMU bypass, or cross-authority sandbox break.\nC:H - This is a use-after-free of struct cred: aa_replace_current_label() drops the task’s refs during override_creds(), then revert_creds() restores a dangling cred pointer. Reclaiming the cred slab yields an arbitrary kernel read. Kernel UAF scores C:H.\nI:H - The same cred UAF is a classic heap-spray primitive on struct cred, enabling arbitrary writes and control-flow hijacking / privilege escalation. Kernel UAF scores I:H.\nA:H - The author reproduced a KASAN use-after-free of current_cred() on a later getuid() after the FUSE splice sequence; dereferencing the freed cred oopses or panics the kernel." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "security/apparmor/include/cred.h", "security/apparmor/include/task.h", "security/apparmor/task.c" ], "versions": [ { "version": "c75afcd153f6147d3b094f45a1d87e5df7f4f053", "lessThan": "361488984d668235438faac28635f3632351407f", "status": "affected", "versionType": "git" }, { "version": "c75afcd153f6147d3b094f45a1d87e5df7f4f053", "lessThan": "587a6a92b93ec314c583bbf747413af170d42540", "status": "affected", "versionType": "git" }, { "version": "c75afcd153f6147d3b094f45a1d87e5df7f4f053", "lessThan": "580f777d6d9fd07fc034bd1aeba5c30fd48871a2", "status": "affected", "versionType": "git" }, { "version": "c75afcd153f6147d3b094f45a1d87e5df7f4f053", "lessThan": "3f4ae5fab613dca01d6a2a8210dd832e009fcf47", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "security/apparmor/include/cred.h", "security/apparmor/include/task.h", "security/apparmor/task.c" ], "versions": [ { "version": "2.6.36", "status": "affected" }, { "version": "0", "lessThan": "2.6.36", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.109", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.50", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.4", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.36", "versionEndExcluding": "6.12.109" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.36", "versionEndExcluding": "6.18.50" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.36", "versionEndExcluding": "7.2.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.36", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "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" } ], "title": "apparmor: fix cred UAF caused by begin_current_label_crit_section()", "x_generator": { "engine": "bippy-1.2.0" } } } }