Description
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, HTMLRenderer.heading() builds the opening <hN> tag by string-concatenating the id attribute value directly into the HTML — with no call to escape(), safe_entity(), or any other sanitisation function. A double-quote character " in the id value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, src=, href=, etc.) into the heading element. This vulnerability is fixed in 3.2.1.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| lepture | mistune | < 3.2.1 | — |
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 +1 | No fix yet | — |
| Ubuntu 26.04 LTS | mistune | No fix yet | — |
| Ubuntu 25.10 | mistune +1 | No fix yet | — |
| Ubuntu 24.04 LTS | mistune | No fix yet | — |
| Ubuntu 22.04 LTS | mistune0 | No fix yet | — |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | mistune | No fix yet | — |
| 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 | 3.2.1-1.1 | openSUSE-SU-2026:10761-1 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | python-mistune | 3.2.1-1 | — |
Wolfi
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Wolfi rolling | kubeflow-pipelines-visualization-server | 2.16.1-r2 | — |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| PyPI | mistune | < 3.2.1 | 3.2.1 | GHSA-v87v-83h2-53w7 |
Advisories 1
- openSUSE-SU-2026:10761-1 python311-mistune-3.2.1-1.1 on GA media SUSE / openSUSE Security Updates · May 13, 2026