CVE Intelligence
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CVE-2026-89644 — btrfs: fix extent map leak in NOCOW direct I/O write

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix extent map leak in NOCOW direct I/O write btrfs_dio_iomap_begin() calls btrfs_get_extent(), which returns an extent map reference that must be dropped on all exit paths. For direct writes into a NOCOW range, btrfs_get_blocks_direct_write() keeps using that extent map and asks btrfs_create_dio_extent() to allocate the ordered extent. If that fails, for example because btrfs_alloc_ordered_extent() fails, the function returns the error without dropping the input extent map. The PREALLOC path avoided this by dropping the input extent map before replacing it with the newly created one. Check the error from btrfs_create_dio_extent() before replacing the map and drop the input extent map on failure.

Published Sep 11, 2026 · Updated Oct 21, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: Linux

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.2% (30-day exploitation probability)+1

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.17%
ahead of 6% of scored CVEs · Oct 22, 2026
Affects
Linux
Linux
CVSS base
—
Score not published yet.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Linux Linux).
  2. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  3. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Linux Linux ≥ 5f9a8a51d8b95505d8de8b7191ae2ed8c504d4af and < b7c873765875645b11503f94c9bae2ca80127375≥ 5f9a8a51d8b95505d8de8b7191ae2ed8c504d4af and < f42efd634c0ae7ba0ce2fc5e30e291b0803b0ae2≥ 5f9a8a51d8b95505d8de8b7191ae2ed8c504d4af and < 05a1a816eef8b3e4332620a64fc8cf45c4eb5c0d≥ 5f9a8a51d8b95505d8de8b7191ae2ed8c504d4af and < 3f950867c307c5413d628a153ac44915bd117ffdversion 4.7≥ 5f9a8a51d8b95505d8de8b7191ae2ed8c504d4af and < cb732d302245b14943a5017015fffa8e6db7a6c0 Vulnerable CVE Program (cve.org) e CISA ADP

EPSS over time FIRST

Oct 15, 2026 → Oct 22, 2026 · 7 reading(s) · max 0.17%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Not enough vector or weakness data: use the affected application’s logs as a starting point.
application logs

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · linux/linux
    Oct 21, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 15, 2026
  • Affected products added · linux/linux
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • Source status changed · → Received
    Oct 15, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 15, 2026 · NIST National Vulnerability Database
  • CVE published
    Sep 11, 2026 · Linux

Source activity

Repeated readings are counted rather than listed.

  • 2× References added · Oct 19, 2026 – Oct 21, 2026
  • 1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

7 on the record

Elsewhere on this site

Linux
every CVE for this vendor

Related CVEs (same products)

  • CVE-2026-99087 dm-integrity: fix NULL pointer dereference when the 'R' flag is used 10h
  • CVE-2026-99086 dm-integrity: validate the superblock on resume 10h
  • CVE-2026-99080 fs: Free any excess xarray nodes in clear_inode() 10h
  • CVE-2026-99079 net/mlx5e: Prevent stale XSK buffer release on refill retry 10h
  • CVE-2026-99081 bnxt_en: fix DMA mapping length for padded small packets 10h
  • CVE-2026-99082 KVM: x86: Use active memslots for the per-vCPU MMIO cache 10h

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No CVSS score published by NVD, the CNA, CISA or GitHub so far.
  • No fixed version, patch or mitigation documented.
  • No CISA SSVC assessment.
  • No CWE classification.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-89644 is "btrfs: fix extent map leak in NOCOW direct I/O write", rated Unknown. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. EPSS 0.17% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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