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CVE Record

CVE-2026-45892: ext4: drop extent cache after doing PARTIAL_VALID1 zeroout

In the Linux kernel, the following vulnerability has been resolved: ext4: drop extent cache after doing PARTIAL_VALID1 zeroout When splitting an unwritten extent in the middle and converting it to initialized in ext4_split_extent() with the EXT4_EXT_MAY_ZEROOUT and EXT4_EXT_DATA_VALID2 flags set, it could leave a stale unwritten extent. Assume we have an unwritten file and buffered write in the middle of it without dioread_nolock enabled, it will allocate blocks as written extent. 0 A B N [UUUUUUUUUUUU] on-disk extent U: unwritten extent [UUUUUUUUUUUU] extent status tree [--DDDDDDDD--] D: valid data |<- ->| ----> this range needs to be initialized ext4_split_extent() first try to split this extent at B with EXT4_EXT_DATA_PARTIAL_VALID1 and EXT4_EXT_MAY_ZEROOUT flag set, but ext4_split_extent_at() failed to split this extent due to temporary lack of space. It zeroout B to N and leave the entire extent as unwritten. 0 A B N [UUUUUUUUUUUU] on-disk extent [UUUUUUUUUUUU] extent status tree [--DDDDDDDDZZ] Z: zeroed data ext4_split_extent() then try to split this extent at A with EXT4_EXT_DATA_VALID2 flag set. This time, it split successfully and leave an written extent from A to N. 0 A B N [UUWWWWWWWWWW] on-disk extent W: written extent [UUUUUUUUUUUU] extent status tree [--DDDDDDDDZZ] Finally ext4_map_create_blocks() only insert extent A to B to the extent status tree, and leave an stale unwritten extent in the status tree. 0 A B N [UUWWWWWWWWWW] on-disk extent W: written extent [UUWWWWWWWWUU] extent status tree [--DDDDDDDDZZ] Fix this issue by always cached extent status entry after zeroing out the second part.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel ext4 filesystem bug where internal bookkeeping can wrongly remember part of a file extent as unwritten after the kernel has converted it. The public record does not state a business impact such as privilege escalation, data loss, or denial of service, so urgency depends on kernel exposure and vendor assessment.

Executive priority

Medium operational priority until severity is clarified: do not treat this as emergency exploitation, but include it in the next kernel patch cycle, especially for Linux systems storing critical data on ext4.

Technical view

The bug is in ext4 extent splitting when EXT4_EXT_MAY_ZEROOUT and EXT4_EXT_DATA_VALID2 are involved after a PARTIAL_VALID1 zeroout. A failed split can zero the second range, then a later successful split updates on-disk extents but leaves a stale unwritten extent in the extent status tree. Stable kernel commits address this by dropping the cached extent status entry.

Likely exposure

Potential exposure is limited to Linux systems using ext4 with kernels containing the affected ext4 code path. The source bundle lists Linux kernel commit identifiers and version 6.1.167, but provides no distribution mapping, CPEs, or default affected product list beyond Linux.

Exploitation context

The CVE record does not report active exploitation, and KEV status is false. The source bundle does not provide exploitability details, attacker prerequisites, or a demonstrated security impact. Treat it as a kernel filesystem correctness issue until vendor advisories clarify impact and severity.

Researcher notes

Key evidence is the kernel description, not an external exploit report. The failure sequence involves ext4_split_extent_at temporary lack of space, zeroing B-to-N, then a successful A split that leaves stale extent status cache state. No CWE, CVSS, or exploit prerequisites are provided.

Mitigation direction

  • Check Linux vendor advisories for CVE-2026-45892 and mapped package versions.
  • Update kernels to versions containing the referenced stable ext4 fixes.
  • Prioritize systems that rely on ext4 for critical data workloads.
  • Avoid direct wrangler-style deployment assumptions; follow normal kernel maintenance controls.
  • Document any temporary risk acceptance where vendor fixes are not yet available.

Validation and detection

  • Inventory Linux kernel versions and ext4 usage across servers and images.
  • Compare installed kernels with vendor advisories and referenced stable commits.
  • Review package changelogs for CVE-2026-45892 or the ext4 fix title.
  • Confirm patched systems boot the expected kernel after maintenance.
  • Track whether vendors assign CVSS, severity, or distribution-specific impact.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
0ADP providers
7Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxddf854e59166533b0f46ba32cd6cd9aca3197d1b, 58ddae5d77b1db3a27b891c75a8fa120239ac092, d17857b4fb9ba5745b59be0ef38fd532991fccbf, d67c8ecf3d8fda9b8ef80e6f665d84b6d6ac9d88, 7015fcf473796e1d2d876f241bd9e0c36f3d4eef, 1bf6974822d1dba86cf11b5f05498581cf3488a2unaffected
LinuxLinux6.1.167unaffected
Weakness

CWE details

No CWE listed

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