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Medium

mistune Cross-site scripting (XSS) vulnerability

  • Disclosed: 29.12.2017
  • Updated: 11.10.2026 11:20

Cross-site scripting (XSS) vulnerability in the _keyify function in mistune.py in Mistune before 0.8.1 allows remote attackers to inject arbitrary web script or HTML by leveraging failure to escape the "key" argument.

Affected software

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PlatformPackageVulnerable versionsFixed in
Python (PyPI) mistune < 0.8.1 0.8.1

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
29.12.2017
Updated
11.10.2026 11:20

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2017-18 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-98gj-wwxm-cj3h - 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 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
  7. Mistune vulnerable to catastrophic backtracking
    High · 8.6 CVE-2022-34749 >= 2.0.0a1, < 2.0.3 2.0.3
  8. mistune Cross-site scripting (XSS) vulnerability this entry
    Medium · 6.1 CVE-2017-16876 < 0.8.1 0.8.1

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