VulnerabilityPublished 28 Oct 2026

CVE-2026-99174: Linux kernel · ext4: free the sbi after a grace period

Source GCVE Database

Authoritative record:CVE-2026-99174

Not known to be exploited · fixed in c17b44266a1f9fcb49b894d4611d1254bf1aa313 : update Linux kernel when convenient.

Data as of 28 Oct 2026, 13:47 UTC

Severity

Medium

Rated Medium by Threat Radar's AI analysis · CVSS not yet scored by NVD

Patch: Available – fixed in c17b44266a1f9fcb49b894d4611d1254bf1aa313, 87d29b8b849738d52fe820d495fa0aa2d5a1ec82, 80d5db1686b05fad6f384be017714297d828a714

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-h9fx-4jcw-948x

What to do

Upgrade Linux kernel to c17b44266a1f9fcb49b894d4611d1254bf1aa313, 87d29b8b849738d52fe820d495fa0aa2d5a1ec82 or 80d5db1686b05fad6f384be017714297d828a714.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 6493792d3299b3e33f887ef8a150099d271faf9c, < c17b44266a1f9fcb49b894d4611d1254bf1aa313	Fixed in c17b44266a1f9fcb49b894d4611d1254bf1aa313
LinuxLinux	Affected ≥ 6493792d3299b3e33f887ef8a150099d271faf9c, < 87d29b8b849738d52fe820d495fa0aa2d5a1ec82	Fixed in 87d29b8b849738d52fe820d495fa0aa2d5a1ec82
LinuxLinux	Affected ≥ 6493792d3299b3e33f887ef8a150099d271faf9c, < 80d5db1686b05fad6f384be017714297d828a714	Fixed in 80d5db1686b05fad6f384be017714297d828a714
LinuxLinux	Affected =5.19	Fixed in–
Red Hatredhat/kernel`pkg:rpm/redhat/kernel`Other threats	Affected =5.19	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

A fix has been implemented that defers freeing the superblock info and extent status counters until after a grace period, preventing use-after-free conditions. Users should apply the official kernel patch that addresses this issue. Until patched, avoiding race conditions involving unmounting and pathwalks may reduce exposure, but no complete workaround is documented.

Description

A use-after-free vulnerability exists in the ext4 filesystem implementation in the Linux kernel. The issue arises because ext4_put_super() frees the superblock information (sbi) and associated counters without waiting for a grace period, potentially allowing a pathwalk in ext4_get_link() to dereference freed memory. This can lead to a null pointer dereference and kernel crash. The vulnerability is difficult to trigger and typically requires a race condition involving the last reference to a mount going away outside of the usual unmount path.

Impact

This vulnerability can cause a kernel null pointer dereference leading to a denial of service (system crash). It does not indicate remote code execution or privilege escalation but can disrupt system stability if triggered. The race condition is hard to reproduce and requires specific timing involving mount references and pathwalks.

Summary

The Linux kernel's ext4 filesystem has a vulnerability where ext4_put_super() prematurely frees the superblock info (sbi) and extent status counters without waiting for a grace period. ext4_get_link() may still be accessing these structures concurrently, leading to a null pointer dereference and kernel crash (KASAN detected). The flaw occurs because ext4_get_link() follows a symlink in RCU pathwalk mode and reads s_mount_state and extent counters through sb->s_fs_info, which ext4_put_super() clears and frees too early. The fix involves deferring the freeing of sbi and counters until after a grace period to avoid use-after-free conditions.

References

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