{"id":"CVE-2025-39840","state":"PUBLISHED","title":"audit: fix out-of-bounds read in audit_compare_dname_path()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\naudit: fix out-of-bounds read in audit_compare_dname_path()\n\nWhen a watch on dir=/ is combined with an fsnotify event for a\nsingle-character name directly under / (e.g., creating /a), an\nout-of-bounds read can occur in audit_compare_dname_path().\n\nThe helper parent_len() returns 1 for \"/\". In audit_compare_dname_path(),\nwhen parentlen equals the full path length (1), the code sets p = path + 1\nand pathlen = 1 - 1 = 0. The subsequent loop then dereferences\np[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.\n\nFix this by adding a pathlen > 0 check to the while loop condition\nto prevent the out-of-bounds access.\n\n[PM: subject tweak, sign-off email fixes]","publishedAt":"2025-09-19T15:26:15.596Z","updatedAt":"2026-08-05T12:05:33.644Z","severity":{"score":7.1,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e92eebb0d6116f942ab25dfb1a41905aa59472a8","status":"affected","lessThan":"9735a9dcc307427e7d6336c54171682f1bac9789","versionType":"git"},{"version":"e92eebb0d6116f942ab25dfb1a41905aa59472a8","status":"affected","lessThan":"4540f1d23e7f387880ce46d11b5cd3f27248bf8d","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/auditfilter.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.14","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.14","versionType":"semver"},{"version":"6.16.6","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/auditfilter.c"]}],"references":["https://git.kernel.org/stable/c/9735a9dcc307427e7d6336c54171682f1bac9789","https://git.kernel.org/stable/c/4540f1d23e7f387880ce46d11b5cd3f27248bf8d"],"weaknesses":["CWE-125"],"ingestedAt":"2026-10-29T20:09:09.358Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/39xxx/CVE-2025-39840.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-39840","state":"PUBLISHED","datePublished":"2025-09-19T15:26:15.596Z","dateUpdated":"2026-08-05T12:05:33.644Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-04-16T07:20:57.141Z"},"containers":{"cna":{"title":"audit: fix out-of-bounds read in audit_compare_dname_path()","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\naudit: fix out-of-bounds read in audit_compare_dname_path()\n\nWhen a watch on dir=/ is combined with an fsnotify event for a\nsingle-character name directly under / (e.g., creating /a), an\nout-of-bounds read can occur in audit_compare_dname_path().\n\nThe helper parent_len() returns 1 for \"/\". In audit_compare_dname_path(),\nwhen parentlen equals the full path length (1), the code sets p = path + 1\nand pathlen = 1 - 1 = 0. The subsequent loop then dereferences\np[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.\n\nFix this by adding a pathlen > 0 check to the while loop condition\nto prevent the out-of-bounds access.\n\n[PM: subject tweak, sign-off email fixes]"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"e92eebb0d6116f942ab25dfb1a41905aa59472a8","status":"affected","lessThan":"9735a9dcc307427e7d6336c54171682f1bac9789","versionType":"git"},{"version":"e92eebb0d6116f942ab25dfb1a41905aa59472a8","status":"affected","lessThan":"4540f1d23e7f387880ce46d11b5cd3f27248bf8d","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/auditfilter.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.14","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.14","versionType":"semver"},{"version":"6.16.6","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["kernel/auditfilter.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/9735a9dcc307427e7d6336c54171682f1bac9789"},{"url":"https://git.kernel.org/stable/c/4540f1d23e7f387880ce46d11b5cd3f27248bf8d"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","baseScore":7.1,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The vulnerable code is reached only through the syscall audit context (`__audit_getname`/`__audit_inode_child`) or an fsnotify event on a locally-installed audit watch, both of which require issuing local syscalls such as symlink()/mkdir()/rename(). No network-facing kernel service (nfsd/ksmbd) builds audit name entries via getname(), so there is no remote path to the defect.\nAC:L - The attacker fully controls both inputs — an all-slash pathname argument and the basename of the created child — so the backwards walk past the start of the buffer is triggered deterministically on every attempt, with no race to win and no timing dependency. Padding the slash string to ≥EMBEDDED_NAME_MAX deterministically forces the string into a page-aligned names_cachep object, so even the page-boundary read is attacker-arranged.\nPR:L - Any unprivileged local user can call symlink(\"///…\", \"/tmp/x\") in a world-writable directory; no capability, namespace trick, or audit privilege is needed, and the AUDIT_TYPE_UNKNOWN found_child branch bypasses the ino/dev ownership check entirely. The only precondition is a system-wide audit ruleset installed by the administrator, which is an environmental condition rather than an attacker privilege.\nUI:N - The attacking process performs the whole sequence itself in a single syscall; no victim has to mount a filesystem, open a file, or take any other action.\nS:U - The out-of-bounds read occurs in kernel heap memory and both the flaw and its consequences stay within the kernel's own security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - This is an out-of-bounds read that is not bounded to a few bytes — the loop keeps decrementing and dereferencing backwards for as long as the preceding kernel memory contains 0x2f bytes, so an attacker who sprays '/' bytes into the heap can extend the walk across adjacent slab objects and pages, touching arbitrary kernel memory beyond the allocation.\nI:N - The defect performs only reads; `pathlen` becomes negative so the comparison always returns \"no match\" and `memcmp()` is unreachable, leaving no memory write, no control-flow influence, and no change to the audit records that would be emitted.\nA:H - With a slash string long enough to occupy a page-aligned 4096-byte names_cachep object, the walk immediately dereferences the byte before a page boundary and can continue across pages, producing a kernel oops on an unmapped/guard page under KFENCE, DEBUG_PAGEALLOC, or a direct-map hole, and a fatal KASAN report on hardened kernels; it is repeatable at will by an unprivileged user."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:05:33.644Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14","versionEndExcluding":"6.16.6"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14","versionEndExcluding":"6.17"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"cvssV3_1":{"scope":"UNCHANGED","version":"3.1","baseScore":7.1,"attackVector":"LOCAL","baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","integrityImpact":"NONE","userInteraction":"NONE","attackComplexity":"LOW","availabilityImpact":"HIGH","privilegesRequired":"LOW","confidentialityImpact":"HIGH"}},{"other":{"type":"ssvc","content":{"id":"CVE-2025-39840","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-01-14T19:20:33.496174Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-125","lang":"en","type":"CWE","description":"CWE-125 Out-of-bounds Read"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-01-14T19:23:12.172Z"}}]}}}