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Vulnerabilities

Vulnerability · CVE-2026-99174

ext4: free the sbi after a grace period

Published Oct 28, 2026 · catalog updated Oct 28, 2026 · Linux Linux

Last checked Nov 3, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-99174. EPSS is 0.18%. Act only if a listed version of Linux Linux is installed.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
High—
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.18%
Remediation
Not established
Affected products
vendor Linux Linux

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->s_fs_info. ext4_put_super() destroys those counters, clears sb->s_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+0xf0/0x640 Call Trace: ext4_get_link+0x26c/0x410 pick_link+0xf96/0x1780 step_into_slowpath+0x9b8/0x1250 path_lookupat+0x484/0xb00 filename_lookup+0x1f1/0x5b0 vfs_statx+0xd7/0x3b0 vfs_fstatat+0x4d/0x90 __do_sys_newfstatat+0xa0/0x100 do_syscall_64+0x10e/0x5e0 entry_SYSCALL_64_after_hwframe+0x77/0x7f 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->s_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.

Are you affected?

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  • vendor Linux Linuxversion unspecified

How to fix CVE-2026-99174

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-99174. EPSS is 0.18%. Act only if a listed version of Linux Linux is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.18%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 28, 2026 · Tenable CVE Database

    Detected

    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 cou

  2. Oct 28, 2026 · CVE.org

    Updated

    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 cou

Sources

  • BSI CERT-BundGovernment advisoryCVE-2026-99174

    Linux Kernel: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff

    wid.cert-bund.de
  • CVE.orgVulnerability recordCVE-2026-99174

    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 th

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-99174

    30-day exploitation probability 0.18%

    first.org
  • Tenable CVE DatabaseVulnerability recordCVE-2026-99174

    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 cou

    tenable.com

References

Freshness

Last verified in this catalog Nov 3, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSOct 31, 2026
  • BSI CERT-BundOct 30, 2026
  • CVE.orgOct 29, 2026
  • Tenable CVE DatabaseOct 28, 2026