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CVE-2026-45892 Linux CVE debrief

A vulnerability in the Linux kernel's ext4 filesystem could leave stale unwritten extent entries in the extent status tree after a partial zeroout operation. When ext4_split_extent() splits an unwritten extent with EXT4_EXT_MAY_ZEROOUT and EXT4_EXT_DATA_PARTIAL_VALID1 flags set, a failed split attempt at one boundary followed by a successful split at another boundary can result in the extent status tree containing stale unwritten extent entries that do not match the on-disk state. This inconsistency between the in-memory extent status tree and on-disk extents could lead to incorrect I/O behavior or data integrity issues. The fix ensures the cached extent status entry is dropped after zeroing out the second part of the extent, preventing the stale entry from persisting.

Vendor
Linux
Product
Unknown
CVSS
MEDIUM 5.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-27
Original CVE updated
2026-06-25
Advisory published
2026-05-27
Advisory updated
2026-06-25

Who should care

Linux system administrators managing ext4 filesystems, particularly those with workloads involving buffered writes to unwritten extents without dioread_nolock enabled; kernel maintainers and distribution security teams tracking ext4 filesystem stability fixes

Technical summary

The vulnerability exists in ext4_split_extent() when handling unwritten extents with the EXT4_EXT_MAY_ZEROOUT and EXT4_EXT_DATA_PARTIAL_VALID1 flags. The code path involves: (1) an initial attempt to split at boundary B that fails due to temporary space constraints, leaving zeroed data from B to N while the entire extent remains marked unwritten; (2) a subsequent successful split at boundary A with EXT4_EXT_DATA_VALID2, creating a written extent from A to N on-disk; (3) ext4_map_create_blocks() only inserting extent A to B into the status tree, leaving a stale unwritten extent entry from B to N. The fix drops the cached extent status entry after the zeroout operation to ensure consistency between the extent status tree and on-disk state.

Defensive priority

medium

Recommended defensive actions

  • Apply kernel updates containing the referenced stable commits when available from your Linux distribution
  • Monitor vendor security advisories for kernel package updates addressing this ext4 filesystem issue
  • Review systems using ext4 filesystems with unwritten extents and buffered I/O workloads for potential data integrity concerns
  • Consider testing critical ext4 workloads on updated kernels before production deployment

Evidence notes

The vulnerability description is sourced from the official CVE record published 2026-05-27. The issue affects the ext4 filesystem implementation in the Linux kernel. Multiple stable kernel commits are referenced, indicating fixes were backported to various kernel versions. No CVSS score or severity rating has been assigned as of the CVE modification date (2026-05-27T14:48:31.480Z).

Sources and references

Verified primary and authoritative sources

  • CVE-2026-45892 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-45892

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-45892 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-45892

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/6d882ea3b0931b43530d44149b79fcd4ffc13030

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/a1b962a821e7a52d48212ae269b45808b4411267

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/c2ee51d684adca7645e4aa74adca13f6750390bc

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/d8ee559fccdef713f058cfe5f2c03dc9b18be3b1

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/f0931a5c17005a0c4fc35bd1a001245effc3354b

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.