{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-21655","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-12-29T08:45:45.729Z","datePublished":"2025-01-20T13:48:40.544Z","dateUpdated":"2026-09-08T08:40:14.559Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T11:53:24.723Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/eventfd: ensure io_eventfd_signal() defers another RCU period\n\nio_eventfd_do_signal() is invoked from an RCU callback, but when\ndropping the reference to the io_ev_fd, it calls io_eventfd_free()\ndirectly if the refcount drops to zero. This isn't correct, as any\npotential freeing of the io_ev_fd should be deferred another RCU grace\nperiod.\n\nJust call io_eventfd_put() rather than open-code the dec-and-test and\nfree, which will correctly defer it another RCU grace period."}],"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 vulnerability is reached through the io_uring_setup/io_uring_register/io_uring_enter syscalls and an eventfd write() from a local process. No network-reachable component processes the affected data.\nAC:L - The attacker controls both sides of the race: it deterministically schedules the RCU callback via a write() to a polled eventfd, then issues UNREGISTER_EVENTFD/ring-close during the multi-millisecond grace period while another thread spins in io_eventfd_grab(), and can retry unboundedly by re-registering a fresh ev_fd.\nPR:L - Only an ordinary unprivileged local user account is needed — sysctl kernel.io_uring_disabled defaults to 0 (io_uring allowed for everyone) and IORING_REGISTER_EVENTFD/IORING_UNREGISTER_EVENTFD perform no capability check.\nUI:N - The attacker performs every step itself — ring setup, eventfd registration, poll arming, the triggering write(), and the unregister. No victim action is involved.\nS:U - The use-after-free corrupts kernel heap memory within the same security authority; there is no VM, IOMMU, or sandbox boundary crossed.\nC:H - The UAF lets a reallocated kmalloc-64 object supply the ->cq_ev_fd pointer, which is dereferenced as a struct eventfd_ctx *, giving attacker-directed kernel reads and, via typical UAF heap-spray techniques, disclosure of arbitrary kernel memory.\nI:H - The stale object yields an atomic RMW on freed memory, an arbitrary-address increment (ctx->count++), a call_rcu() on freed memory, and a wake_up_locked_poll() walking an attacker-controlled waitqueue whose func pointer is invoked — a control-flow hijack primitive enabling privilege escalation.\nA:H - Freeing io_ev_fd a grace period early reliably produces kernel oops/panic from the UAF read, the atomic RMW on freed memory, and RCU callback-list corruption."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["io_uring/eventfd.c"],"versions":[{"version":"21a091b970cdbcf3e8ff829234b51be6f9192766","lessThan":"6b63308c28987c6010b1180c72a6db4df6c68033","status":"affected","versionType":"git"},{"version":"21a091b970cdbcf3e8ff829234b51be6f9192766","lessThan":"8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10","status":"affected","versionType":"git"},{"version":"21a091b970cdbcf3e8ff829234b51be6f9192766","lessThan":"a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7","status":"affected","versionType":"git"},{"version":"21a091b970cdbcf3e8ff829234b51be6f9192766","lessThan":"c9a40292a44e78f71258b8522655bffaf5753bdb","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["io_uring/eventfd.c"],"versions":[{"version":"6.1","status":"affected"},{"version":"0","lessThan":"6.1","status":"unaffected","versionType":"semver"},{"version":"6.1.125","lessThanOrEqual":"6.1.*","status":"unaffected","versionType":"semver"},{"version":"6.6.72","lessThanOrEqual":"6.6.*","status":"unaffected","versionType":"semver"},{"version":"6.12.10","lessThanOrEqual":"6.12.*","status":"unaffected","versionType":"semver"},{"version":"6.13","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":"6.1","versionEndExcluding":"6.1.125"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.1","versionEndExcluding":"6.6.72"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.1","versionEndExcluding":"6.12.10"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.1","versionEndExcluding":"6.13"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/6b63308c28987c6010b1180c72a6db4df6c68033"},{"url":"https://git.kernel.org/stable/c/8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10"},{"url":"https://git.kernel.org/stable/c/a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7"},{"url":"https://git.kernel.org/stable/c/c9a40292a44e78f71258b8522655bffaf5753bdb"},{"url":"https://project-zero.issues.chromium.org/issues/388499293"}],"title":"io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period","x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CVE Program Container","references":[{"url":"https://lists.debian.org/debian-lts-announce/2025/03/msg00001.html"}],"providerMetadata":{"orgId":"af854a3a-2127-422b-91ae-364da2661108","shortName":"CVE","dateUpdated":"2025-11-03T20:58:34.729Z"}},{"x_adpType":"supplier","providerMetadata":{"orgId":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e","shortName":"siemens-SADP","dateUpdated":"2026-09-08T08:40:14.559Z"},"affected":[{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP","versions":[{"status":"affected","version":"V3.1.6","lessThan":"*","versionType":"custom"}],"defaultStatus":"unknown"},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP","versions":[{"status":"affected","version":"V3.1.6","lessThan":"*","versionType":"custom"}],"defaultStatus":"unknown"},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP","versions":[{"status":"affected","version":"V3.1.6","lessThan":"*","versionType":"custom"}],"defaultStatus":"unknown"},{"vendor":"Siemens","product":"SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP","versions":[{"status":"affected","version":"V3.1.6","lessThan":"*","versionType":"custom"}],"defaultStatus":"unknown"},{"vendor":"Siemens","product":"SIPLUS S7-1500 CPU 1518-4 PN/DP MFP","versions":[{"status":"affected","version":"V3.1.6","lessThan":"*","versionType":"custom"}],"defaultStatus":"unknown"}],"references":[{"url":"https://cert-portal.siemens.com/productcert/html/ssa-019113.html"}]}]}}