Description
Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| lepture | mistune | 3.0.0 – < 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 | — |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | python-mistune | 3.4.0-2.1 | openSUSE-SU-2026:12407-1 |
Advisories 1
- openSUSE-SU-2026:12407-1 python313-mistune-3.4.0-2.1 on GA media SUSE / openSUSE Security Updates · Nov 4, 2026
References
- GitHub Security Advisory (GHSA-x2gr-6qf2-fc9x) vendor-advisory
- VulnCheck Advisory: Mistune before 3.3.0 Quadratic-Time DoS via parse_link_text third-party-advisory