CVE-2026-80537 (GCVE-0-2026-80537)

Vulnerability from cvelistv5 – Published: 2026-08-26 14:37 – Updated: 2026-08-27 05:01
VLAI
Title
xfs: fix off-by-one in rtrefcount btree root level validation
Summary
In the Linux kernel, the following vulnerability has been resolved: xfs: fix off-by-one in rtrefcount btree root level validation xfs_rtrefcountbt_compute_maxlevels() sets mp->m_rtrefc_maxlevels = min(d_maxlevels, r_maxlevels) + 1; where the trailing "+ 1" already accounts for the inode-root level, so the deepest valid on-disk root level is m_rtrefc_maxlevels - 1 and a cursor must satisfy bc_nlevels <= bc_maxlevels (= m_rtrefc_maxlevels). The two on-disk validation paths, xfs_rtrefcountbt_verify() and xfs_iformat_rtrefcount(), check the root level with ">" instead of ">=", so a crafted rtreflink (metadir + realtime + reflink) image whose /rtgroups/N.refcount inode has bb_level == m_rtrefc_maxlevels is accepted on mount. xfs_rtrefcountbt_init_cursor() then sets bc_nlevels = bb_level + 1, exceeding bc_maxlevels by one. Since the xfs_rtrefcountbt_cur slab object is sized for exactly bc_maxlevels entries, the first btree op on such a cursor indexes bc_levels[m_rtrefc_maxlevels] past the end of the object. This is reached by the first rtrefcount cursor built after mount, via log/CoW recovery (xfs_reflink_recover_cow() during xfs_mountfs()) or an FS_IOC_GETFSMAP over the realtime device. Reject a root level equal to m_rtrefc_maxlevels, matching the ">=" form already used by the sibling data-device refcount/rmap verifiers and the in-memory rtrmap verifier. BUG: KASAN: slab-out-of-bounds in xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101) Write of size 2 at addr ffff888018391658 by task exploit/144 xfs_btree_lookup (fs/xfs/libxfs/xfs_btree.c:2101) xfs_btree_query_range (fs/xfs/libxfs/xfs_btree.c:5308) xfs_refcount_recover_cow_leftovers (fs/xfs/libxfs/xfs_refcount.c:2113) xfs_reflink_recover_cow (fs/xfs/xfs_reflink.c:1085) xlog_recover_finish (fs/xfs/xfs_log_recover.c:3551) xfs_mountfs (fs/xfs/xfs_mount.c:1158) xfs_fs_fill_super (fs/xfs/xfs_super.c:1940) get_tree_bdev_flags (fs/super.c:1634) vfs_get_tree (fs/super.c:1694) path_mount (fs/namespace.c:4161) __x64_sys_mount (fs/namespace.c:4367) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) The buggy address belongs to the cache xfs_rtrefcountbt_cur of size 216 The buggy address is located 8 bytes to the right of allocated 216-byte region [ffff888018391578, ffff888018391650) Kernel panic - not syncing: Fatal exception
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 9abe03a0e4f978615a2b1b484b8d09ca84c16ea0 , < 8a0ecae2ecda9f9a83a496ed05c42c4b1f5c3f2d (git)
Affected: 9abe03a0e4f978615a2b1b484b8d09ca84c16ea0 , < ccebfc309441e0b37b2e6ece90f18810a489d326 (git)
Affected: 9abe03a0e4f978615a2b1b484b8d09ca84c16ea0 , < cc3144da377de5fb422d44a2311f978623f7c900 (git)
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Linux Linux Affected: 6.14
Unaffected: 0 , < 6.14 (semver)
Unaffected: 6.18.46 , ≤ 6.18.* (semver)
Unaffected: 7.1.10 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/xfs/libxfs/xfs_rtrefcount_btree.c"
          ],
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          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "9abe03a0e4f978615a2b1b484b8d09ca84c16ea0",
              "versionType": "git"
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            {
              "lessThan": "ccebfc309441e0b37b2e6ece90f18810a489d326",
              "status": "affected",
              "version": "9abe03a0e4f978615a2b1b484b8d09ca84c16ea0",
              "versionType": "git"
            },
            {
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              "status": "affected",
              "version": "9abe03a0e4f978615a2b1b484b8d09ca84c16ea0",
              "versionType": "git"
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        {
          "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-\u003em_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 \u003c= bc_maxlevels (= m_rtrefc_maxlevels).\n\nThe two on-disk validation paths, xfs_rtrefcountbt_verify() and\nxfs_iformat_rtrefcount(), check the root level with \"\u003e\" instead of \"\u003e=\", 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 \"\u003e=\" 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\u2014mount(2) during xfs_reflink_recover_cow() in xfs_mountfs(), or FS_IOC_GETFSMAP on an already-mounted XFS volume\u2014not 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",
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  "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",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-80537",
      "date": "2026-09-01",
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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 \\\"\u003e=\\\" 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\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"fs/xfs/libxfs/xfs_rtrefcount_btree.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"9abe03a0e4f978615a2b1b484b8d09ca84c16ea0\",\"lessThan\":\"8a0ecae2ecda9f9a83a496ed05c42c4b1f5c3f2d\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"9abe03a0e4f978615a2b1b484b8d09ca84c16ea0\",\"lessThan\":\"ccebfc309441e0b37b2e6ece90f18810a489d326\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"9abe03a0e4f978615a2b1b484b8d09ca84c16ea0\",\"lessThan\":\"cc3144da377de5fb422d44a2311f978623f7c900\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"fs/xfs/libxfs/xfs_rtrefcount_btree.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"6.14\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"6.14\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.46\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1.10\",\"lessThanOrEqual\":\"7.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"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}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/8a0ecae2ecda9f9a83a496ed05c42c4b1f5c3f2d\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/cc3144da377de5fb422d44a2311f978623f7c900\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/ccebfc309441e0b37b2e6ece90f18810a489d326\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-27T06:34:04+00:00",
      "cve": "CVE-2026-80537",
      "id": "CVE-2026-80537",
      "initial_release_date": "2026-08-26T00:00:00+00:00",
      "product_status:known_affected": "76",
      "product_status:known_not_affected": "198",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: xfs: fix off-by-one in rtrefcount btree root level validation",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-80537.json",
      "version": "3"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
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Detection rules are retrieved from Rulezet.