{ "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": "2026-08-05T11:53:24.723Z" }, "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": "2026-07-14T12:39:38.450Z" }, "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" } ] } ] } }