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Medium

Mistune has XSS via unescaped figclass/figwidth in Figure directive

  • Disclosed: 08.05.2026
  • Updated: 11.10.2026 15:17

In src/mistune/directives/image.py, the render_figure() function concatenates figclass and figwidth options directly into HTML attributes without escaping (lines 152-168).

This allows attribute injection and XSS even when HTMLRenderer(escape=True) is used, because these values bypass the inline renderer.

Other attributes in the same file (src, alt, style) are properly escaped; figclass/figwidth were missed.

Affected software

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PlatformPackageVulnerable versionsFixed in
Python (PyPI) mistune < 3.2.1 3.2.1

References

CVSS score 6.1/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Weakness (CWE)
CWE-79
Platform
Python (PyPI)
Package
mistune
Disclosed
08.05.2026
Updated
11.10.2026 15:17

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2026-168 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-58cw-g322-p94v - CC BY 4.0

Vulnerability history: mistune

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (20) in the archive
Total entries
20
First → latest
10.2017 09.2026
Without a fix
1
Exploited in attacks
0

Severity breakdown

  • High 7
  • Medium 13

Disclosures per year

Severity:
  1. Mistune: Denial of Service — RecursionError via Excessive Emphasis Markers in Markdown
    High · 7.5 CVE-2026-76098 >= 3.3.0, < 3.3.3 3.3.3
  2. Mistune: Potential DoS via quadratic-time parsing in parse_link_text
    High · 7.5 CVE-2026-49851 < 3.3.0 3.3.0
  3. Mistune inline_parser: quadratic-time parsing on long runs of `**x**` and `***x***` emphasis pairs
    High · 7.5 CVE-2026-59925 < 3.3.0 3.3.0
  4. Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions
    High · 7.5 CVE-2026-59928 < 3.3.0 3.3.0
  5. Mistune plugins/formatting: quadratic-time parsing on long runs of `~~x~~`, `==x==`, and `^^x^^` markers (strikethrough / mark / insert)
    High · 7.5 CVE-2026-59922 < 3.3.0 3.3.0
  6. Mistune has XSS via unescaped figclass/figwidth in Figure directive this entry
    Medium · 6.1 CVE-2026-44896 < 3.2.1 3.2.1
  7. Mistune has a ReDoS in LINK_TITLE_RE that allows denial of service via crafted Markdown input
    High CVE-2026-33079 >= 3.0.0a1, < 3.2.1 3.2.1
  8. Mistune vulnerable to catastrophic backtracking
    High · 8.6 CVE-2022-34749 >= 2.0.0a1, < 2.0.3 2.0.3

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