VulnerabilityPublished 11 Sep 2026Updated 5 Oct 2026

CVE-2026-89772: Linux kernel · btrfs: write-protect folios during data writeback

Affects Linux kernelSource GCVE Database

Not known to be exploited.

Data as of 26 Oct 2026, 12:55 UTC

Severity

Medium

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 9% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation evidence

Disclosed: evidence found.
CVE published 11 Sep 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-xrh7-4f5f-76f9

What to do

Affected software

Product	Affected	Fixed in
Ubuntu 26.04 LTSlinux`pkg:deb/ubuntu/linux?arch=source&distro=resolute`Other threats	Affected 6.17.0-5.5 – 7.0.0-38.38 23 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-aws`pkg:deb/ubuntu/linux-aws?arch=source&distro=resolute`Other threats	Affected 6.17.0-1002.2 – 7.0.0-1014.14 15 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-azure`pkg:deb/ubuntu/linux-azure?arch=source&distro=resolute`Other threats	Affected 6.17.0-1003.3 – 7.0.0-1017.17 15 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-azure-fde`pkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resolute`Other threats	Affected 7.0.0-1003.3 – 7.0.0-1016.16 9 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-gcp`pkg:deb/ubuntu/linux-gcp?arch=source&distro=resolute`Other threats	Affected 6.17.0-1002.2 – 7.0.0-1014.14 13 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-gke`pkg:deb/ubuntu/linux-gke?arch=source&distro=resolute`Other threats	Affected 7.0.0-1002.3 – 7.0.0-1008.9 6 affected builds	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 for this vulnerability has been implemented in the Linux kernel by restoring the write-protection calls (folio_clear_dirty_for_io()) during data writeback in Btrfs. Users should update to the patched kernel versions listed to mitigate this issue. No additional mitigation steps are required beyond applying the official fix.

Description

A vulnerability in the Linux kernel's Btrfs filesystem writeback process allows a process with a memory-mapped file to modify data during writeback without triggering expected protections. This can lead to data corruption, lost writes, invalid checksums, and corrupted compressed data. The issue arises from missing write-protection calls on folios during partial or batch writeback operations, especially affecting large folios, subpage sectors, zoned submissions, inline extents, and compressed extents. Multiple concrete bugs can manifest, including lost writes even after fsync(), corrupted compressed data, and persistence of zeroed bytes past EOF. The vulnerability affects specific Linux kernel versions listed and has been resolved by restoring appropriate write-protection calls.

Impact

The vulnerability can cause data corruption, lost writes even after fsync(), invalid checksums, and corrupted compressed data in the Btrfs filesystem. Processes with mmap-ed files can modify data during writeback without triggering faults, leading to unstable folios and inconsistent data states. This affects file integrity and reliability on affected Linux kernel versions.

Summary

The vulnerability (CVE-2026-89772) in the Linux kernel's Btrfs filesystem involves the improper handling of folio write-protection during data writeback. A patch replaced the folio_clear_dirty_for_io() call with a simpler folio_test_dirty() check, omitting the write-protection step (folio_mkclean()) that prevents modifications during writeback. This omission allows processes with mmap-ed files to modify sectors during writeback without faulting, causing data corruption, lost writes, invalid checksums, and corrupted compressed extents. The issue affects scenarios including large folios, subpage sectors, zoned submissions, inline extents, folios spanning EOF, and compressed extents. The vulnerability was introduced by a patch series and has been fixed by reintroducing the necessary write-protection calls to ensure data integrity during writeback.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Oct 2026, 03:42 UTC

Technical details

References

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