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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| lepture | mistune | < 3.3.0 | 3.3.0 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | mistune | No fix yet | — |
| Debian 13 | mistune | No fix yet | — |
| Debian 12 | mistune | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | mistune | No fix yet | — |
| Ubuntu 26.04 LTS | mistune | No fix yet | — |
| Ubuntu 24.04 LTS | mistune | No fix yet | — |
| Ubuntu 22.04 LTS | mistune | No fix yet | — |
| Ubuntu 20.04 LTS | mistune | No fix yet | — |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 18.04 LTS | mistune | No fix yet | — |
| Ubuntu 16.04 LTS | mistune | No fix yet | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | python3-mistune | 0.8.3-14.amzn2023.0.5 | ALAS2023-2026-3386 |
Advisories 1
- ALAS2023-2026-3386 Important: python-mistune security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Nov 9, 2026
References
- GitHub Security Advisory (GHSA-xrpv-r66x-8p7j) vendor-advisory
- VulnCheck Advisory: Mistune before 3.3.0 Quadratic-Time DoS via Unmatched Brackets in Inline Parser third-party-advisory