{
  "cveId": "CVE-2026-99174",
  "url": "https://patchblox.com/security/cve/CVE-2026-99174",
  "summary": "CVE-2026-99174 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-99174, released November 3, 2026. It is not reported as exploited. Patch Radar priority: High.",
  "title": "ext4: free the sbi after a grace period",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  ext4: free the sbi after a grace period  ext4_get_link() follows a symlink that keeps its target in a data block in rcu pathwalk mode with ext4_getblk(EXT4_GET_BLOCKS_CACHED_NOWAIT). That reads s_mount_state in the ASSERT() of ext4_getblk() and again in ext4_es_lookup_extent(), and the lookup bumps the extent status hit or miss counter, all through sb-\u003Es_fs_info.  ext4_put_super() destroys those counters, clears sb-\u003Es_fs_info and frees the sbi without waiting for a grace period. A pathwalk that is still in ext4_get_link() when the last reference to the mount goes away then dereferences a NULL s_fs_info, the freed sbi or the destroyed percpu counters.  With a pathwalk held up in ext4_get_link() while the last reference goes away:    KASAN: null-ptr-deref in range [0x00000000000000a8-0x00000000000000af]   RIP: 0010:ext4_getblk\u002B0xf0/0x640   Call Trace:    \u003CTASK\u003E    ext4_get_link\u002B0x26c/0x410    pick_link\u002B0xf96/0x1780    step_into_slowpath\u002B0x9b8/0x1250    path_lookupat\u002B0x484/0xb00    filename_lookup\u002B0x1f1/0x5b0    vfs_statx\u002B0xd7/0x3b0    vfs_fstatat\u002B0x4d/0x90    __do_sys_newfstatat\u002B0xa0/0x100    do_syscall_64\u002B0x10e/0x5e0    entry_SYSCALL_64_after_hwframe\u002B0x77/0x7f  So far that has been hard to hit. umount(2) waits for a grace period in namespace_unlock() before it drops the mount, so only a mount whose last reference goes away elsewhere, like the close of a file or a chdir out of a lazily unmounted directory, can race a walker.  Keep sb-\u003Es_fs_info and free the sbi together with the extent status counters after a grace period. Split the counters out of ext4_es_unregister_shrinker() for that. The shrinker still gets wasted in ext4_put_super(), the counters go with the sbi.",
  "published": "2026-10-28T11:17:38Z",
  "severity": "Moderate",
  "cvss": 7.1,
  "epss": 0.00179,
  "epssPercentile": 0.07521,
  "priority": "High",
  "priorityTier": 3,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "vendorAdvisory": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-99174",
  "fixes": [
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 13.5 (trixie)",
      "fixedVersion": "6.12.115-2",
      "fix": "DEBIAN-CVE-2026-99174",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-99174",
      "released": "2026-11-03T18:58:21Z"
    },
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 14",
      "fixedVersion": "7.2.13-1",
      "fix": "DEBIAN-CVE-2026-99174",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2026-99174",
      "released": "2026-11-03T18:58:21Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-08T06:59:42Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}