{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-72170", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-08-09T03:40:39.910Z", "datePublished": "2026-08-15T05:53:36.332Z", "dateUpdated": "2026-08-23T12:46:59.271Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-23T12:46:59.271Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\n9p: skip nlink update in cacheless mode to fix WARN_ON\n\nv9fs_dec_count() unconditionally calls drop_nlink() on regular files,\neven when the inode's nlink is already zero. In cacheless mode the\nclient refetches inode metadata from the server (the source of truth)\non every operation, so by the time v9fs_remove() returns, the locally\ncached nlink may already reflect the post-unlink value:\n\n 1. Client initiates unlink, server processes it and sets nlink to 0\n 2. Client refetches inode metadata (nlink=0) before unlink returns\n 3. Client's v9fs_remove() completes successfully\n 4. Client calls v9fs_dec_count() which calls drop_nlink() on nlink=0\n\nThis race is easily triggered under heavy unlink workloads, such as\nstress-ng's unlink stressor, producing the following warning:\n\n WARNING: fs/inode.c:417 at drop_nlink+0x4c/0xc8\n Call trace:\n drop_nlink+0x4c/0xc8\n v9fs_remove+0x1e0/0x250 [9p]\n v9fs_vfs_unlink+0x20/0x38 [9p]\n vfs_unlink+0x13c/0x258\n ...\n\nIn cacheless mode the server is authoritative and the inode is on its\nway out, so locally adjusting nlink buys nothing. Skip v9fs_dec_count()\nentirely when neither CACHE_META nor CACHE_LOOSE is set, which both\navoids the warning and removes a class of nlink races (two concurrent\nunlinkers observing nlink > 0 and both calling drop_nlink()) that an\nnlink == 0 guard alone would only narrow rather than close." } ], "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 - Triggered via unlink/rmdir/rename syscalls on a mounted 9p client filesystem (default cacheless mode). Common in QEMU/KVM virtio-9p guest shares and TCP-mounted exports; requires code execution on the client host, not direct remote packet delivery to this kernel path.\nAC:L - The fix commit states the race is easily triggered under heavy unlink workloads (e.g., stress-ng). An attacker can drive concurrent unlinks or getattr/unlink on the same inode to refresh server nlink=0 before drop_nlink(), controlling both sides of the race.\nPR:L - Exploitation requires only normal filesystem write permission on the 9p export (may_delete_dentry/inode_permission on the parent directory). Guest users on virtio-9p shares or tenants with write access do not need root/CAP_SYS_ADMIN beyond using an already-mounted filesystem.\nUI:N - No victim interaction is required beyond the attacker (or compromised local process) issuing unlink/rmdir/rename on paths they can already write; mounting 9p is an admin setup step, not per-exploit user action.\nS:U - The bug corrupts inode metadata in the 9p client kernel on the same host as the attacker process. It does not cross VM/host, container/host, or IOMMU security boundaries; virtio-9p guest triggers affect the guest kernel only.\nC:H - drop_nlink() on i_nlink==0 emits WARN_ON then underflows the unsigned link counter to UINT_MAX, corrupting kernel inode metadata. Per kernel CVSS guidance, memory/metadata corruption that could be leveraged for further exploitation warrants High confidentiality.\nI:H - Unsigned i_nlink underflow corrupts inode lifecycle accounting, preventing correct removal tracking (s_remove_count) and desynchronizing dentry unlink from inode state. This class of VFS inode corruption can enable further integrity violations and is scored High when uncertain.\nA:H - Each hit triggers kernel WARN_ON (easily spammed for denial-of-service via log flooding, and fatal where panic_on_warn is enabled) and leaves inodes with bogus nlink values that can provoke subsequent kernel faults during VFS operations on affected files." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/9p/vfs_inode.c" ], "versions": [ { "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb", "lessThan": "6086469f7d469549bfd070348b717a6e43736200", "status": "affected", "versionType": "git" }, { "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb", "lessThan": "ab257019cb72f467b55c95384d99c94e3908b928", "status": "affected", "versionType": "git" }, { "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb", "lessThan": "4ec4ebe40c82cb4c60756732f6593055d010c59c", "status": "affected", "versionType": "git" }, { "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb", "lessThan": "a5a682b016ef5b5384e28f6d652d47a8f8e73d37", "status": "affected", "versionType": "git" }, { "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb", "lessThan": "de79c3f3643841b8659a71958df7cf2a66bfd409", "status": "affected", "versionType": "git" }, { "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb", "lessThan": "8d610017c992de705b304d3d727a6e3a86af6149", "status": "affected", "versionType": "git" }, { "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb", "lessThan": "8faccac11e1369adddf5d80f4a45af93f13b2e1a", "status": "affected", "versionType": "git" }, { "version": "ac89b2ef9b55924bcf922251f043ba73a32d05bb", "lessThan": "574aa0b4799470ac814479f1138d19efe6262255", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/9p/vfs_inode.c" ], "versions": [ { "version": "4.17", "status": "affected" }, { "version": "0", "lessThan": "4.17", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.266", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.217", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.184", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.145", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.97", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.40", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1.5", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2", "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": "4.17", "versionEndExcluding": "5.10.266" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.17", "versionEndExcluding": "5.15.217" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.17", "versionEndExcluding": "6.1.184" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.17", "versionEndExcluding": "6.6.145" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.17", "versionEndExcluding": "6.12.97" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.17", "versionEndExcluding": "6.18.40" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.17", "versionEndExcluding": "7.1.5" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.17", "versionEndExcluding": "7.2" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/6086469f7d469549bfd070348b717a6e43736200" }, { "url": "https://git.kernel.org/stable/c/ab257019cb72f467b55c95384d99c94e3908b928" }, { "url": "https://git.kernel.org/stable/c/4ec4ebe40c82cb4c60756732f6593055d010c59c" }, { "url": "https://git.kernel.org/stable/c/a5a682b016ef5b5384e28f6d652d47a8f8e73d37" }, { "url": "https://git.kernel.org/stable/c/de79c3f3643841b8659a71958df7cf2a66bfd409" }, { "url": "https://git.kernel.org/stable/c/8d610017c992de705b304d3d727a6e3a86af6149" }, { "url": "https://git.kernel.org/stable/c/8faccac11e1369adddf5d80f4a45af93f13b2e1a" }, { "url": "https://git.kernel.org/stable/c/574aa0b4799470ac814479f1138d19efe6262255" } ], "title": "9p: skip nlink update in cacheless mode to fix WARN_ON", "x_generator": { "engine": "bippy-1.2.0" } } } }