{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89791","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-09-11T19:38:34.766Z","datePublished":"2026-09-16T08:48:27.020Z","dateUpdated":"2026-09-16T14:38:40.190Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-09-16T14:38:40.190Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nperf: Fix use-after-free when perf mmap() revival races with the last munmap()\n\nperf_mmap_close() drops rb->mmap_count *without* holding\nevent->mmap_mutex (the refcount_dec_and_test() right before the\nrefcount_dec_and_mutex_lock() of event->mmap_count). A concurrent\nperf_mmap_rb() can slot its entire \"revival\" path into that window\n(perf_mmap holds event->mmap_mutex for its whole duration, including\nrb_alloc):\n\n  munmap side (perf_mmap_close)          mmap side (perf_mmap_rb)\n  -----------------------------------    --------------------------------\n  rb->mmap_count 1 -> 0   (no lock)      (holds event->mmap_mutex)\n                                         inc_not_zero(rb->mmap_count) fails\n                                         ring_buffer_attach(event, NULL)\n                                         rb_alloc() + attach new rb\n                                         refcount_set(&event->mmap_count, 1)\n  lock; event->mmap_count 1 -> 0\n  ring_buffer_attach(event, NULL)\n  ring_buffer_put() -> frees the *new* rb\n\nThe revival's refcount_set(&event->mmap_count, 1) is an invisible\n1 -> 1 write: the close frees the just-revived buffer although the\nother process still has it mapped -- a page-level use-after-free\nallowing local privilege escalation to root by any unprivileged user\n(default kernel.perf_event_paranoid=2).\n\nSwap the order of the two counter updates: event->mmap_count is\ndropped first via refcount_dec_and_mutex_lock(), so its 1 -> 0\ntransition and the ring_buffer_attach() stay serialized with\nperf_mmap(). rb->mmap_count == 0 then implies every event using the\nbuffer is detached already, so the result of the rb->mmap_count drop\ncan gate the remaining teardown directly and detach_rest is no longer\nneeded.\n\nAn earlier fix for this race from Kyle Zeng and David Lee takes\nevent->mmap_mutex around both counter updates [0]; here the not-last\nclose stays lockless."}],"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 - The UAF is reached only via local syscalls: perf_event_open(2) then mmap(2)/munmap(2) on the resulting perf fd (perf_fops.mmap → perf_mmap → perf_mmap_rb racing perf_mmap_close). There is no network, adjacent-radio, or physical path into the ring-buffer revival race.\nAC:L - The attacker drives both sides from threads or processes sharing the fd: one munmap() runs perf_mmap_close() while a concurrent mmap() holds event->mmap_mutex through rb_alloc() and map_range(). That is an attacker-controlled, freely retryable race, not an uninfluenced layout or victim-state condition.\nPR:L - Default kernel.perf_event_paranoid=2 still allows an unprivileged per-task software event with exclude_kernel set; perf_mmap() only calls the optional LSM security_perf_event_read hook and does not require CAP_PERFMON or CAP_SYS_ADMIN. The fix notes local privilege escalation by any unprivileged user.\nUI:N - The attacker opens the event and races mmap/munmap on that fd in their own process or a helper that inherited the fd. No victim action such as mounting a filesystem or opening a file is required.\nS:U - Impact is host-kernel page use-after-free of the perf ring buffer, i.e. standard local privilege escalation in the same OS security authority. It is not a KVM/Xen guest-to-host escape or IOMMU/DMA boundary bypass.\nC:H - perf_mmap_close() frees the revived ring-buffer pages (rb_free) while the concurrent mmap's VM_PFNMAP VMA still maps those PFNs. That page-level UAF lets the attacker reclaim the pages and read arbitrary kernel memory through the still-valid mapping.\nI:H - The same still-mapped PFNs remain writable on the user control page (perf_mmap_pfn_mkwrite), so reclaim/spray of the freed pages yields a kernel write primitive. The fix commit describes this as local privilege escalation to root, matching UAF integrity High.\nA:H - Use-after-free of the ring buffer while it remains mapped causes kernel oops or panic on reuse, and the reporters documented a panic reproducer. Any kernel UAF is availability High even without a completed privilege-escalation exploit."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/events/core.c"],"versions":[{"version":"59741451b49ce9964a9758c19d6f7df2a1255c75","lessThan":"929cb3b9dc818dd9fa89d510d4ff2b255e42badd","status":"affected","versionType":"git"},{"version":"59741451b49ce9964a9758c19d6f7df2a1255c75","lessThan":"0c739f54f1c77f3a4643160cd2e031b6c2f2aab6","status":"affected","versionType":"git"},{"version":"59741451b49ce9964a9758c19d6f7df2a1255c75","lessThan":"58a8108bc73de0740d5b88150465d6690ea5f85f","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/events/core.c"],"versions":[{"version":"6.18","status":"affected"},{"version":"0","lessThan":"6.18","status":"unaffected","versionType":"semver"},{"version":"6.18.52","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.2.5","lessThanOrEqual":"7.2.*","status":"unaffected","versionType":"semver"},{"version":"7.3-rc2","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":"6.18","versionEndExcluding":"6.18.52"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18","versionEndExcluding":"7.2.5"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.18","versionEndExcluding":"7.3-rc2"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/929cb3b9dc818dd9fa89d510d4ff2b255e42badd"},{"url":"https://git.kernel.org/stable/c/0c739f54f1c77f3a4643160cd2e031b6c2f2aab6"},{"url":"https://git.kernel.org/stable/c/58a8108bc73de0740d5b88150465d6690ea5f85f"}],"title":"perf: Fix use-after-free when perf mmap() revival races with the last munmap()","x_generator":{"engine":"bippy-1.2.0"}}}}