{"cve":"CVE-2026-80537","nvd":{"published":"2026-08-26T15:17:07.890","modified":"2026-08-27T06:17:34.210","status":"Received","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","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8},"cwes":[],"references":["https://git.kernel.org/stable/c/8a0ecae2ecda9f9a83a496ed05c42c4b1f5c3f2d","https://git.kernel.org/stable/c/cc3144da377de5fb422d44a2311f978623f7c900","https://git.kernel.org/stable/c/ccebfc309441e0b37b2e6ece90f18810a489d326"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:50:17.453294893+00:00"},"epss":{"cve":"CVE-2026-80537","score":0.00173,"percentile":0.06759,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}