Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, rendertocul() builds a <ul> table-of-contents tree from a list of (level, id, text) tuples. Both the id value (used as href="#<id>") and the text value (used as the visible link label) are inserted into <a> tags via a plain Python format string — with no HTML escaping applied to either value. When heading IDs are derived from user-supplied heading text (the standard use-case for readable slug anchors), an attacker can craft a heading whose text breaks out of the href="#..." attribute context, injecting arbitrary HTML tags including <script> blocks directly into the rendered TOC. This vulnerability is fixed in 3.2.1.
{
"cwe_ids": [
"CWE-79"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/44xxx/CVE-2026-44898.json"
}{
"cpe": "cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*",
"source": [
"AFFECTED_FIELD",
"CPE_RANGE",
"REFERENCES"
],
"extracted_events": [
{
"introduced": "0"
},
{
"fixed": "3.2.1"
}
]
}