CVE intelligence and bounded remediation
CVE-2026-44899 — Mistune is a Python Markdown parser with renderers and plugins
Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, the Image directive plugin validates the :width: and :height: options with a regex compiled as _num_re = re.compile(r"^\d+(?:\.\d*)?"). When the validated value is not a plain integer, render_block_image() inserts it directly into a style="width:...;" or style="height:...;" attribute. Because the value was accepted by the prefix-only regex, any CSS after the leading digits reaches the style= attribute verbatim and without escaping. This vulnerability is fixed in 3.2.1.
- Severity
- Medium
- CVSS
- 6.1 (3.1)
- Published
- 2026-05-26
- CISA KEV
- Not currently listed
- Ecosystem
- python/pypi
- Weaknesses
- CWE-79
Affected products
- mistune_project / mistune
Matched remediation archetype
Cross-site scripting and unsafe browser output
This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.
Check exposure
- Trace reflected, stored, and DOM-derived untrusted values into HTML, attributes, URLs, styles, scripts, and client-side template sinks.
- Identify affected origins, authenticated user roles, sensitive browser capabilities, and where content is shared across tenants.
- Review framework escaping, rich-text sanitization, legacy templates, and client-side rendering paths.
Remediate safely
- Use context-aware framework output encoding and safe DOM APIs; keep untrusted data out of executable contexts.
- Sanitize intentionally supported markup with a maintained allowlist policy and validate URLs and attributes separately.
- Update affected rendering components and add tests for every output context using inert sentinel markup.
Authoritative sources
Complete CVE record and remediation plan
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