{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-47124","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-03-04T18:12:48.839Z","datePublished":"2024-03-15T20:14:29.605Z","dateUpdated":"2026-08-05T08:46:08.931Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T08:46:08.931Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring: fix link timeout refs\n\nWARNING: CPU: 0 PID: 10242 at lib/refcount.c:28 refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28\nRIP: 0010:refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28\nCall Trace:\n __refcount_sub_and_test include/linux/refcount.h:283 [inline]\n __refcount_dec_and_test include/linux/refcount.h:315 [inline]\n refcount_dec_and_test include/linux/refcount.h:333 [inline]\n io_put_req fs/io_uring.c:2140 [inline]\n io_queue_linked_timeout fs/io_uring.c:6300 [inline]\n __io_queue_sqe+0xbef/0xec0 fs/io_uring.c:6354\n io_submit_sqe fs/io_uring.c:6534 [inline]\n io_submit_sqes+0x2bbd/0x7c50 fs/io_uring.c:6660\n __do_sys_io_uring_enter fs/io_uring.c:9240 [inline]\n __se_sys_io_uring_enter+0x256/0x1d60 fs/io_uring.c:9182\n\nio_link_timeout_fn() should put only one reference of the linked timeout\nrequest, however in case of racing with the master request's completion\nfirst io_req_complete() puts one and then io_put_req_deferred() is\ncalled."}],"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 bug is in io_uring's linked-timeout hrtimer path (io_link_timeout_fn), reached only via local io_uring_setup/io_uring_enter syscalls after submitting IORING_OP_LINK_TIMEOUT, not via network packet processing.\nAC:L - The race is between master-request completion and the linked-timeout hrtimer; the attacker controls both sides by choosing the linked operation and timeout duration and can retry until the double-put hits.\nPR:L - Any unprivileged local user can create an io_uring and submit linked timeouts; io_uring_setup has no CAP_SYS_ADMIN gate for this path (CAP_IPC_LOCK is only for locked-memory accounting).\nUI:N - Exploitation requires only the attacker's own io_uring submissions; no victim action such as mounting a filesystem or opening a crafted file is needed.\nS:U - A successful exploit yields corruption or control within the local kernel authority (typical local privilege escalation), not a cross-boundary escape such as guest-to-host or IOMMU bypass.\nC:H - The bug double-puts the linked-timeout io_kiocb (atomic_t refs, no saturation), freeing it then touching it again—a use-after-free that can be reused for arbitrary kernel memory disclosure.\nI:H - Use-after-free of a slab-allocated io_kiocb enables heap reuse and write primitives suitable for control-flow hijacking or arbitrary kernel memory modification, as with related io_uring linked-timeout UAFs.\nA:H - The double-put underflows request refs and can free or corrupt the object while still in use, reliably causing kernel warnings, oopses, or crashes (and worse under exploitation)."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/io_uring.c"],"versions":[{"version":"1c20e9040f49687ba2ccc2ffd4411351a6c2ebff","lessThan":"0b2a990e5d2f76d020cb840c456e6ec5f0c27530","status":"affected","versionType":"git"},{"version":"1c20e9040f49687ba2ccc2ffd4411351a6c2ebff","lessThan":"6f5d7a45f58d3abe3a936de1441b8d6318f978ff","status":"affected","versionType":"git"},{"version":"9ae1f8dd372e0e4c020b345cf9e09f519265e981","lessThan":"876808dba2ff7509bdd7f230c4f374a0caf4f410","status":"affected","versionType":"git"},{"version":"9ae1f8dd372e0e4c020b345cf9e09f519265e981","lessThan":"ff4a96ba5c8f9b266706280ff8021d2ef3f17e86","status":"affected","versionType":"git"},{"version":"9ae1f8dd372e0e4c020b345cf9e09f519265e981","lessThan":"a298232ee6b9a1d5d732aa497ff8be0d45b5bd82","status":"affected","versionType":"git"},{"version":"567c81912cec641db75ac6cb64c63f8367c97d19","status":"affected","versionType":"git"},{"version":"5.10.26","lessThan":"5.10.43","status":"affected","versionType":"semver"},{"version":"5.10.26","lessThan":"5.10.55","status":"affected","versionType":"semver"},{"version":"5.11.6","lessThan":"5.12","status":"affected","versionType":"semver"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/io_uring.c"],"versions":[{"version":"5.12","status":"affected"},{"version":"0","lessThan":"5.12","status":"unaffected","versionType":"semver"},{"version":"5.10.43","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.10.55","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.12.10","lessThanOrEqual":"5.12.*","status":"unaffected","versionType":"semver"},{"version":"5.12.19","lessThanOrEqual":"5.12.*","status":"unaffected","versionType":"semver"},{"version":"5.13","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":"5.10.26","versionEndExcluding":"5.10.43"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.10.26","versionEndExcluding":"5.10.55"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"5.12.10"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"5.12.19"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.12","versionEndExcluding":"5.13"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.11.6"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/0b2a990e5d2f76d020cb840c456e6ec5f0c27530"},{"url":"https://git.kernel.org/stable/c/6f5d7a45f58d3abe3a936de1441b8d6318f978ff"},{"url":"https://git.kernel.org/stable/c/876808dba2ff7509bdd7f230c4f374a0caf4f410"},{"url":"https://git.kernel.org/stable/c/ff4a96ba5c8f9b266706280ff8021d2ef3f17e86"},{"url":"https://git.kernel.org/stable/c/a298232ee6b9a1d5d732aa497ff8be0d45b5bd82"}],"title":"io_uring: 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