{"api_version":"1","generated_at":"2026-08-28T16:11:11+00:00","cve":"CVE-2026-80537","urls":{"html":"https://cve.report/CVE-2026-80537","api":"https://cve.report/api/cve/CVE-2026-80537.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-80537","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-80537"},"summary":{"title":"xfs: fix off-by-one in rtrefcount btree root level validation","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nxfs: fix off-by-one in rtrefcount btree root level validation\n\nxfs_rtrefcountbt_compute_maxlevels() sets\n\n\tmp->m_rtrefc_maxlevels = min(d_maxlevels, r_maxlevels) + 1;\n\nwhere the trailing \"+ 1\" already accounts for the inode-root level, so the\ndeepest valid on-disk root level is m_rtrefc_maxlevels - 1 and a cursor must\nsatisfy bc_nlevels <= bc_maxlevels (= m_rtrefc_maxlevels).\n\nThe two on-disk validation paths, xfs_rtrefcountbt_verify() and\nxfs_iformat_rtrefcount(), check the root level with \">\" instead of \">=\", so a\ncrafted rtreflink (metadir + realtime + reflink) image whose\n/rtgroups/N.refcount inode has bb_level == m_rtrefc_maxlevels is accepted on\nmount. xfs_rtrefcountbt_init_cursor() then sets bc_nlevels = bb_level + 1,\nexceeding bc_maxlevels by one. Since the xfs_rtrefcountbt_cur slab object is\nsized for exactly bc_maxlevels entries, the first btree op on such a cursor\nindexes bc_levels[m_rtrefc_maxlevels] past the end of the object. This is\nreached by the first rtrefcount cursor built after mount, via log/CoW\nrecovery (xfs_reflink_recover_cow() during xfs_mountfs()) or an\nFS_IOC_GETFSMAP over the realtime device.\n\nReject a root level equal to m_rtrefc_maxlevels, matching the \">=\" form\nalready used by the sibling data-device refcount/rmap verifiers and the\nin-memory rtrmap verifier.\n\n  BUG: KASAN: slab-out-of-bounds in xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)\n  Write of size 2 at addr ffff888018391658 by task exploit/144\n   xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)\n   xfs_btree_query_range (fs/xfs/libxfs/xfs_btree.c:5308)\n   xfs_refcount_recover_cow_leftovers (fs/xfs/libxfs/xfs_refcount.c:2113)\n   xfs_reflink_recover_cow (fs/xfs/xfs_reflink.c:1085)\n   xlog_recover_finish (fs/xfs/xfs_log_recover.c:3551)\n   xfs_mountfs (fs/xfs/xfs_mount.c:1158)\n   xfs_fs_fill_super (fs/xfs/xfs_super.c:1940)\n   get_tree_bdev_flags (fs/super.c:1634)\n   vfs_get_tree (fs/super.c:1694)\n   path_mount (fs/namespace.c:4161)\n   __x64_sys_mount (fs/namespace.c:4367)\n   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)\n  The buggy address belongs to the cache xfs_rtrefcountbt_cur of size 216\n  The buggy address is located 8 bytes to the right of\n   allocated 216-byte region [ffff888018391578, ffff888018391650)\n  Kernel panic - not syncing: Fatal exception","state":"PUBLISHED","assigner":"Linux","published_at":"2026-08-26 15:17:07","updated_at":"2026-08-27 06:17:34"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"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","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"baseScore":7.8,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"}}],"references":[{"url":"https://git.kernel.org/stable/c/ccebfc309441e0b37b2e6ece90f18810a489d326","name":"https://git.kernel.org/stable/c/ccebfc309441e0b37b2e6ece90f18810a489d326","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/cc3144da377de5fb422d44a2311f978623f7c900","name":"https://git.kernel.org/stable/c/cc3144da377de5fb422d44a2311f978623f7c900","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/8a0ecae2ecda9f9a83a496ed05c42c4b1f5c3f2d","name":"https://git.kernel.org/stable/c/8a0ecae2ecda9f9a83a496ed05c42c4b1f5c3f2d","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-80537","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-80537","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 9abe03a0e4f978615a2b1b484b8d09ca84c16ea0 8a0ecae2ecda9f9a83a496ed05c42c4b1f5c3f2d git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 9abe03a0e4f978615a2b1b484b8d09ca84c16ea0 ccebfc309441e0b37b2e6ece90f18810a489d326 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 9abe03a0e4f978615a2b1b484b8d09ca84c16ea0 cc3144da377de5fb422d44a2311f978623f7c900 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.14","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.14 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.46 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.1.10 7.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"80537","cve":"CVE-2026-80537","epss":"0.001270000","percentile":"0.026430000","score_date":"2026-08-27","updated_at":"2026-08-28 00:03:39"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["fs/xfs/libxfs/xfs_rtrefcount_btree.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"8a0ecae2ecda9f9a83a496ed05c42c4b1f5c3f2d","status":"affected","version":"9abe03a0e4f978615a2b1b484b8d09ca84c16ea0","versionType":"git"},{"lessThan":"ccebfc309441e0b37b2e6ece90f18810a489d326","status":"affected","version":"9abe03a0e4f978615a2b1b484b8d09ca84c16ea0","versionType":"git"},{"lessThan":"cc3144da377de5fb422d44a2311f978623f7c900","status":"affected","version":"9abe03a0e4f978615a2b1b484b8d09ca84c16ea0","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["fs/xfs/libxfs/xfs_rtrefcount_btree.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"6.14"},{"lessThan":"6.14","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.46","versionType":"semver"},{"lessThanOrEqual":"7.1.*","status":"unaffected","version":"7.1.10","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.2","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.46","versionStartIncluding":"6.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.10","versionStartIncluding":"6.14","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2","versionStartIncluding":"6.14","vulnerable":true}],"negate":false,"operator":"OR"}]}],"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nxfs: fix off-by-one in rtrefcount btree root level validation\n\nxfs_rtrefcountbt_compute_maxlevels() sets\n\n\tmp->m_rtrefc_maxlevels = min(d_maxlevels, r_maxlevels) + 1;\n\nwhere the trailing \"+ 1\" already accounts for the inode-root level, so the\ndeepest valid on-disk root level is m_rtrefc_maxlevels - 1 and a cursor must\nsatisfy bc_nlevels <= bc_maxlevels (= m_rtrefc_maxlevels).\n\nThe two on-disk validation paths, xfs_rtrefcountbt_verify() and\nxfs_iformat_rtrefcount(), check the root level with \">\" instead of \">=\", so a\ncrafted rtreflink (metadir + realtime + reflink) image whose\n/rtgroups/N.refcount inode has bb_level == m_rtrefc_maxlevels is accepted on\nmount. xfs_rtrefcountbt_init_cursor() then sets bc_nlevels = bb_level + 1,\nexceeding bc_maxlevels by one. Since the xfs_rtrefcountbt_cur slab object is\nsized for exactly bc_maxlevels entries, the first btree op on such a cursor\nindexes bc_levels[m_rtrefc_maxlevels] past the end of the object. This is\nreached by the first rtrefcount cursor built after mount, via log/CoW\nrecovery (xfs_reflink_recover_cow() during xfs_mountfs()) or an\nFS_IOC_GETFSMAP over the realtime device.\n\nReject a root level equal to m_rtrefc_maxlevels, matching the \">=\" form\nalready used by the sibling data-device refcount/rmap verifiers and the\nin-memory rtrmap verifier.\n\n  BUG: KASAN: slab-out-of-bounds in xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)\n  Write of size 2 at addr ffff888018391658 by task exploit/144\n   xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)\n   xfs_btree_query_range (fs/xfs/libxfs/xfs_btree.c:5308)\n   xfs_refcount_recover_cow_leftovers (fs/xfs/libxfs/xfs_refcount.c:2113)\n   xfs_reflink_recover_cow (fs/xfs/xfs_reflink.c:1085)\n   xlog_recover_finish (fs/xfs/xfs_log_recover.c:3551)\n   xfs_mountfs (fs/xfs/xfs_mount.c:1158)\n   xfs_fs_fill_super (fs/xfs/xfs_super.c:1940)\n   get_tree_bdev_flags (fs/super.c:1634)\n   vfs_get_tree (fs/super.c:1694)\n   path_mount (fs/namespace.c:4161)\n   __x64_sys_mount (fs/namespace.c:4367)\n   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)\n  The buggy address belongs to the cache xfs_rtrefcountbt_cur of size 216\n  The buggy address is located 8 bytes to the right of\n   allocated 216-byte region [ffff888018391578, ffff888018391650)\n  Kernel panic - not syncing: Fatal exception"}],"metrics":[{"cvssV3_1":{"baseScore":7.8,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","version":"3.1"},"scenarios":[{"lang":"en","value":"AV:L - The bug is reached only through local kernel entry points—mount(2) during xfs_reflink_recover_cow() in xfs_mountfs(), or FS_IOC_GETFSMAP on an already-mounted XFS volume—not via any network-facing protocol handler (NFS/ksmbd/SMB/TCP).\nAC:L - An attacker fully controls the crafted rtreflink image and can set /rtgroups/N.refcount bb_level == m_rtrefc_maxlevels so mount or the first rtrefcount cursor reliably drives xfs_btree_lookup() to write past bc_levels[]; no victim-dependent race or layout luck is required.\nPR:L - Triggering mount of a loop-backed crafted image needs only CAP_SYS_ADMIN inside a user namespace (unshare -Urn), which unprivileged users can obtain on typical systems; FS_IOC_GETFSMAP is additionally reachable with only a readable open file on the mounted filesystem.\nUI:N - In the highest-impact scenario an unprivileged attacker mounts their own malicious XFS image in a user namespace and immediately hits CoW recovery during xfs_mountfs(), with no separate victim action beyond routine local code execution.\nS:U - Exploitation corrupts kernel heap metadata and can panic or compromise the host kernel, but does not cross a CVSS scope boundary such as a VM/hypervisor guest-to-host escape or IOMMU/DMA sandbox breakout.\nC:H - KASAN reports a slab out-of-bounds write in xfs_btree_lookup() past the xfs_rtrefcountbt_cur allocation; such heap corruption can disclose or influence adjacent slab objects and is treated as arbitrary memory-read potential under kernel CVSS guidance.\nI:H - The vulnerability is an out-of-bounds write (2 bytes into bc_levels[m_rtrefc_maxlevels]) on a kmalloc slab cursor object, enabling adjacent-object corruption and further heap shaping toward arbitrary kernel write or code execution.\nA:H - The reported reproducer causes KASAN slab-out-of-bounds followed by kernel panic during mount recovery; any host mounting or querying the malicious rtrefcount metadata can crash or deny service to the entire system."}]}],"providerMetadata":{"dateUpdated":"2026-08-27T05:01:27.352Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/8a0ecae2ecda9f9a83a496ed05c42c4b1f5c3f2d"},{"url":"https://git.kernel.org/stable/c/ccebfc309441e0b37b2e6ece90f18810a489d326"},{"url":"https://git.kernel.org/stable/c/cc3144da377de5fb422d44a2311f978623f7c900"}],"title":"xfs: fix off-by-one in rtrefcount btree root level validation","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-80537","datePublished":"2026-08-26T14:37:12.180Z","dateReserved":"2026-08-26T14:34:25.765Z","dateUpdated":"2026-08-27T05:01:27.352Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-08-26 15:17:07","lastModifiedDate":"2026-08-27 06:17:34","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"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","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":5.9}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"80537","Ordinal":"1","Title":"xfs: fix off-by-one in rtrefcount btree root level validation","CVE":"CVE-2026-80537","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"80537","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nxfs: fix off-by-one in rtrefcount btree root level validation\n\nxfs_rtrefcountbt_compute_maxlevels() sets\n\n\tmp->m_rtrefc_maxlevels = min(d_maxlevels, r_maxlevels) + 1;\n\nwhere the trailing \"+ 1\" already accounts for the inode-root level, so the\ndeepest valid on-disk root level is m_rtrefc_maxlevels - 1 and a cursor must\nsatisfy bc_nlevels <= bc_maxlevels (= m_rtrefc_maxlevels).\n\nThe two on-disk validation paths, xfs_rtrefcountbt_verify() and\nxfs_iformat_rtrefcount(), check the root level with \">\" instead of \">=\", so a\ncrafted rtreflink (metadir + realtime + reflink) image whose\n/rtgroups/N.refcount inode has bb_level == m_rtrefc_maxlevels is accepted on\nmount. xfs_rtrefcountbt_init_cursor() then sets bc_nlevels = bb_level + 1,\nexceeding bc_maxlevels by one. Since the xfs_rtrefcountbt_cur slab object is\nsized for exactly bc_maxlevels entries, the first btree op on such a cursor\nindexes bc_levels[m_rtrefc_maxlevels] past the end of the object. This is\nreached by the first rtrefcount cursor built after mount, via log/CoW\nrecovery (xfs_reflink_recover_cow() during xfs_mountfs()) or an\nFS_IOC_GETFSMAP over the realtime device.\n\nReject a root level equal to m_rtrefc_maxlevels, matching the \">=\" form\nalready used by the sibling data-device refcount/rmap verifiers and the\nin-memory rtrmap verifier.\n\n  BUG: KASAN: slab-out-of-bounds in xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)\n  Write of size 2 at addr ffff888018391658 by task exploit/144\n   xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101)\n   xfs_btree_query_range (fs/xfs/libxfs/xfs_btree.c:5308)\n   xfs_refcount_recover_cow_leftovers (fs/xfs/libxfs/xfs_refcount.c:2113)\n   xfs_reflink_recover_cow (fs/xfs/xfs_reflink.c:1085)\n   xlog_recover_finish (fs/xfs/xfs_log_recover.c:3551)\n   xfs_mountfs (fs/xfs/xfs_mount.c:1158)\n   xfs_fs_fill_super (fs/xfs/xfs_super.c:1940)\n   get_tree_bdev_flags (fs/super.c:1634)\n   vfs_get_tree (fs/super.c:1694)\n   path_mount (fs/namespace.c:4161)\n   __x64_sys_mount (fs/namespace.c:4367)\n   entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)\n  The buggy address belongs to the cache xfs_rtrefcountbt_cur of size 216\n  The buggy address is located 8 bytes to the right of\n   allocated 216-byte region [ffff888018391578, ffff888018391650)\n  Kernel panic - not syncing: Fatal exception","Type":"Description","Title":"xfs: fix off-by-one in rtrefcount btree root level validation"}]}}}