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VulnerabilityPublished Updated

CVE-2025-21658: Linux kernel · NULL Pointer Dereference

Affects Linux kernelSource GCVE Database

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Not known to be exploited · CVSS 5.5 Medium.

Data as of 30 Oct 2026, 14:18 UTC

CVSS 3.1 base score
5.5Medium
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CISA-ADPCVSS 3.15.5
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 21 Jan 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq 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 30 Oct 2026.

What to do

AI-suggested

A fix is available in Linux kernel versions including and after the commit that added a check for a valid extent root in scrub_find_fill_first_stripe(). Users running kernels older than 6.6 should manually backport the fix. Until patched, avoid performing scrub operations on corrupted Btrfs filesystems mounted with rescue options. Monitor vendor advisories for updated kernel releases containing the fix.

Description

CVE-2025-21658 is a vulnerability in the Linux kernel's Btrfs filesystem that causes a NULL pointer dereference when no valid extent tree is present. This occurs during a scrub operation on a corrupted filesystem image mounted with rescue options. The flaw leads to a kernel crash (NULL pointer dereference) due to missing validation of the extent root pointer in the scrub_find_fill_first_stripe() function. The issue has been fixed by adding a check for a valid extent root early in the function.

References

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