VulnerabilityPublished 11 Sep 2026Updated 5 Oct 2026

CVE-2026-89644: Linux kernel · btrfs: fix extent map leak in NOCOW direct I/O write

Affects Linux kernelSource GCVE Database

Authoritative record:CVE-2026-89644

Not known to be exploited.

Data as of 26 Oct 2026, 13:47 UTC

Severity

Medium

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 6% 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-8844-3wf4-22v2

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 has been applied to the Linux kernel to address this extent map leak. Users should update to a patched kernel version that includes this fix. The affected versions are explicitly listed and should be upgraded to a fixed version. No additional mitigation steps are indicated.

Description

A vulnerability in the Linux kernel's btrfs filesystem component was fixed to address an extent map reference leak during NOCOW direct I/O writes. The issue occurred when an error during ordered extent allocation caused the function to return without properly dropping the extent map reference, potentially leading to resource leaks.

Impact

This vulnerability causes an extent map reference leak in the btrfs filesystem during NOCOW direct I/O writes when ordered extent allocation fails. While the description does not specify direct exploitation consequences such as privilege escalation or data corruption, resource leaks can degrade system stability or performance over time.

Summary

The Linux kernel's btrfs_dio_iomap_begin() function calls btrfs_get_extent(), which returns an extent map reference that must be released on all exit paths. In the case of direct writes into a NOCOW (No Copy-On-Write) range, btrfs_get_blocks_direct_write() uses this extent map and calls btrfs_create_dio_extent() to allocate the ordered extent. If allocation fails, the function returned an error without dropping the input extent map, causing a leak. The fix ensures that the extent map reference is dropped on failure before returning, aligning with the behavior in the PREALLOC path.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 6 Oct 2026, 13:21 UTC

Technical details

References

Community reviews

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