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CVE-2026-45999 Linux CVE debrief

A vulnerability in the Linux kernel's EROFS (Enhanced Read-Only File System) implementation could allow an attacker with a crafted filesystem image to trigger an out-of-bounds read during LZ4 decompression. The issue stems from an unsigned integer underflow in `z_erofs_lz4_handle_overlap()` when processing malformed extents that specify `m_llen < m_plen` without the `partial_decoding` flag. This causes the inplace decompression path to be incorrectly selected, where the calculation `outpages - inpages` wraps to a large unsigned value, leading to reads past the `decompressed_pages` array boundary. The vulnerability was resolved by adding an additional validation check to prevent this code path from being reached with illegal extent parameters.

Vendor
Linux
Product
Unknown
CVSS
HIGH 7.1
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-27
Original CVE updated
2026-06-19
Advisory published
2026-05-27
Advisory updated
2026-06-19

Who should care

Linux system administrators, kernel maintainers, and security teams managing systems that may mount untrusted or external EROFS filesystem images. Organizations using container or embedded Linux deployments with EROFS support should prioritize patching.

Technical summary

The EROFS filesystem driver in the Linux kernel contains an unsigned integer underflow vulnerability in the LZ4 decompression handler. When processing crafted filesystem images with malformed extent headers (specifically `!partial_decoding && m_llen < m_plen`), the code incorrectly enters an inplace decompression path that cannot handle cases where output pages are fewer than input pages. The subtraction `outpages - inpages` underflows to a large value, causing subsequent array accesses to read beyond allocated memory. The fix adds proper validation to prevent reaching this vulnerable code path with illegal extent parameters.

Defensive priority

medium

Recommended defensive actions

  • Apply kernel updates containing the referenced stable tree commits when available from your Linux distribution
  • Restrict mounting of untrusted EROFS filesystem images
  • Consider disabling EROFS support if not required in your environment
  • Monitor for kernel security advisories from your distribution regarding this CVE

Evidence notes

The vulnerability description indicates that crafted EROFS images with illegal extent parameters can trigger the vulnerable code path. A reproducible test image was provided in the original disclosure (base64-encoded gzipped blob). The fix adds validation to prevent the inplace decompression path from being taken when `outpages < inpages` would occur.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-45999 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-45999

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

  • CVE-2026-45999 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-45999

    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/21e161de2dc660b1bb70ef5b156ab8e6e1cca3ab

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

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/43a878639b90e9721ffa5eb616a7e6d8454adef3

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

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/bbbbb3f0d7864238a8da2a94cd6ec013fee06a2e

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

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/c9ce18e6bb2c467ec85756dc7989b547b7584fee

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

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/f1374fa6e57fd836623668d782ded9244cfd2938

    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.