{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31586","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-03-09T15:48:24.120Z","datePublished":"2026-04-24T14:42:14.937Z","dateUpdated":"2026-08-05T12:23:37.101Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T12:23:37.101Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm: blk-cgroup: fix use-after-free in cgwb_release_workfn()\n\ncgwb_release_workfn() calls css_put(wb->blkcg_css) and then later accesses\nwb->blkcg_css again via blkcg_unpin_online().  If css_put() drops the last\nreference, the blkcg can be freed asynchronously (css_free_rwork_fn ->\nblkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the\npointer to access blkcg->online_pin, resulting in a use-after-free:\n\n  BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n  Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531\n   Workqueue: cgwb_release cgwb_release_workfn\n   Call Trace:\n    <TASK>\n     blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)\n     cgwb_release_workfn (mm/backing-dev.c:629)\n     process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385)\n\n   Freed by task 1016:\n    kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561)\n    css_free_rwork_fn (kernel/cgroup/cgroup.c:5542)\n    process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385)\n\n** Stack based on commit 66672af7a095 (\"Add linux-next specific files\nfor 20260410\")\n\nI am seeing this crash sporadically in Meta fleet across multiple kernel\nversions.  A full reproducer is available at:\nhttps://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh\n\n(The race window is narrow.  To make it easily reproducible, inject a\nmsleep(100) between css_put() and blkcg_unpin_online() in\ncgwb_release_workfn().  With that delay and a KASAN-enabled kernel, the\nreproducer triggers the splat reliably in less than a second.)\n\nFix this by moving blkcg_unpin_online() before css_put(), so the\ncgwb's CSS reference keeps the blkcg alive while blkcg_unpin_online()\naccesses it."}],"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 vulnerable path is reached by local cgroup/writeback activity: creating/removing cgroup v2 subgroups, moving a task into them, and dirtying files on a block-backed filesystem. There is no network or physical packet/device entry point.\nAC:L - Although the timing window is narrow, the attacker can repeatedly drive both cgroup teardown and cgwb creation/release through cgroup churn and buffered writes. Per the scoring rule for attacker-driven races and UAFs, this is low complexity.\nPR:L - The attacker needs local ability to manipulate a delegated cgroup subtree and run file I/O, which is available to low-privileged users in reasonable delegated cgroup v2 or container/user-slice deployments. It does not require real init-namespace root in those scenarios.\nUI:N - No victim action is required once the attacker has local execution and cgroup access. The attacker triggers creation, writeback, and removal directly.\nS:U - The vulnerability is in the host kernel’s cgroup/writeback lifetime management and impacts the same kernel security authority. Standard local kernel privilege escalation is scored as unchanged scope.\nC:H - The bug is a use-after-free of a freed blkcg object after css_put can lead to blkcg_css_free and kfree before blkcg_unpin_online dereferences it. Kernel UAFs are scored high for confidentiality because reclaimed slab contents can be abused for memory disclosure primitives.\nI:H - The immediate UAF performs a refcount decrement/write through freed memory, and reclaimed-object corruption can plausibly be shaped into broader kernel heap corruption or control-flow compromise. Kernel UAF memory corruption is scored high for integrity.\nA:H - The reported failure is a slab-use-after-free in a kernel worker and can cause an oops, panic, or persistent kernel instability. Repeated local triggering makes availability impact high."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/backing-dev.c"],"versions":[{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","lessThan":"23acef4156c260e8598397a1a2e8b3a23e919893","status":"affected","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","lessThan":"1bd36e93b542d9dd020190c6607c6a3663405195","status":"affected","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","lessThan":"740ba1ebb223f137ff088ab74d533a13f9167bd8","status":"affected","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","lessThan":"115a5266749dcde7fe4127e8623d19c752088f69","status":"affected","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","lessThan":"dfc8292a1d6782c76b626315605e0585a5a18447","status":"affected","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","lessThan":"ea3af09eb87d8f8708c66747fcf1a2762902e839","status":"affected","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","lessThan":"50879a3c1faf06e661090015d59e2127255cff27","status":"affected","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","lessThan":"67cb119d32f35e32acd0393bbeb318b2bb1fdafe","status":"affected","versionType":"git"},{"version":"59b57717fff8b562825d9d25e0180ad7e8048ca9","lessThan":"8f5857be99f1ed1fa80991c72449541f634626ee","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["mm/backing-dev.c"],"versions":[{"version":"4.19","status":"affected"},{"version":"0","lessThan":"4.19","status":"unaffected","versionType":"semver"},{"version":"5.10.258","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.15.209","lessThanOrEqual":"5.15.*","status":"unaffected","versionType":"semver"},{"version":"6.1.175","lessThanOrEqual":"6.1.*","status":"unaffected","versionType":"semver"},{"version":"6.6.136","lessThanOrEqual":"6.6.*","status":"unaffected","versionType":"semver"},{"version":"6.12.83","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.18.24","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"6.19.14","lessThanOrEqual":"6.19.*","status":"unaffected","versionType":"semver"},{"version":"7.0.1","lessThanOrEqual":"7.0.*","status":"unaffected","versionType":"semver"},{"version":"7.1","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":"4.19","versionEndExcluding":"5.10.258"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"5.15.209"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.1.175"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.6.136"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.12.83"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.18.24"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.19.14"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"7.0.1"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"7.1"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/23acef4156c260e8598397a1a2e8b3a23e919893"},{"url":"https://git.kernel.org/stable/c/1bd36e93b542d9dd020190c6607c6a3663405195"},{"url":"https://git.kernel.org/stable/c/740ba1ebb223f137ff088ab74d533a13f9167bd8"},{"url":"https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69"},{"url":"https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447"},{"url":"https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839"},{"url":"https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27"},{"url":"https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe"},{"url":"https://git.kernel.org/stable/c/8f5857be99f1ed1fa80991c72449541f634626ee"}],"title":"mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()","x_generator":{"engine":"bippy-1.2.0"}}}}