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CVE-2026-45942 Linux CVE debrief

A race condition in the Linux kernel's ext4 filesystem between page migration and bitmap modification can cause bitmap inconsistency reports and potential data corruption. The vulnerability exists in the ext4_mb_load_buddy() fast path, which only increments folio reference counts without acquiring the folio lock, allowing concurrent folio migration to interfere with bitmap operations. The fix modifies load_buddy to check folio lock status and use the slow path (which acquires the lock) when the folio is locked, closing the concurrency window. This also resolves a false positive corruption error when DOUBLE_CHECK macro is enabled.

Vendor
Linux
Product
Unknown
CVSS
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-27
Original CVE updated
2026-06-24
Advisory published
2026-05-27
Advisory updated
2026-06-24

Who should care

Linux system administrators running ext4 filesystems, particularly those using huge-page workloads or memory-intensive applications; kernel maintainers and distribution security teams responsible for stable kernel updates; organizations with high-availability storage systems where filesystem integrity is critical

Technical summary

The ext4 filesystem's multiblock allocator (mballoc) contains a race condition in ext4_mb_load_buddy() where the fast path increments folio reference counts without holding the folio lock. This allows concurrent page migration (which acquires folio_lock) to race with bitmap modification operations. The vulnerability manifests as bitmap inconsistency errors (e.g., 'group 350, 8179 free clusters as per group info. But got 8192 blocks') and can lead to filesystem corruption. The fix adds a folio lock status check to force the slow path when the folio is locked, ensuring proper synchronization. A secondary issue with the DOUBLE_CHECK macro producing false positive corruption reports is also resolved by this change.

Defensive priority

high

Recommended defensive actions

  • Apply kernel updates containing the referenced stable commits to affected systems
  • Monitor ext4 filesystem logs for bitmap inconsistency reports indicating potential exploitation
  • Consider disabling huge-page workloads on critical ext4 filesystems until patched
  • Enable filesystem integrity monitoring to detect anomalous bitmap state changes
  • Review kernel crash dumps for ext4_mb_complex_scan_group errors with mismatched free cluster counts

Evidence notes

The vulnerability was resolved in the Linux kernel ext4 subsystem. Multiple stable kernel commits address this issue across supported branches. The race condition was observed during stress tests with mixed huge-page workloads, demonstrating practical exploitability despite the narrow timing window.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-45942 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-45942

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

  • CVE-2026-45942 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-45942

    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/29a07d691d282faf38c33d4b61839b89399110f9

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

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/57e83bfbe1e412ac42daced2086f3c6f9a17bba0

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

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/bdc56a9c46b2a99c12313122b9352b619a2e719e

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

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/c05033cfc5c7699cd4df8d48cef94d01da755f24

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

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/f29709a7a3fc38f5015d850504762cdef0e151f9

    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.