What’s Vulnerable › Vulnerabilities

CVE-2019-25781: Python-Markdown 3.0 through 3.11.2 Denial of Service via Link Bracket Parsing

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-29 · updated 2026-10-29
• Weakness: CWE-407

Description

Python-Markdown 3.0 through 3.11.2 contains an algorithmic complexity vulnerability in inline link parsing that allows remote attackers to exhaust CPU through unmatched brackets. Attackers can submit short Markdown containing repeated [ or ![ characters, forcing LinkInlineProcessor.getText() and getLink() into quadratic scans that keep workers busy for minutes.

Affected products

• Python-Markdown Markdown: from 3.0 through 3.11.2

References

• https://github.com/Python-Markdown/markdown
• https://github.com/Python-Markdown/markdown/blob/b41e0aaf1181f1a8cb200cf5a815aad7c0020d23/markdown/inlinepatterns.py#L1155-L1172
• https://github.com/Python-Markdown/markdown/issues/1654
• https://github.com/Python-Markdown/markdown/issues/798
• https://www.vulncheck.com/advisories/python-markdown-3.0-through-3.11.2-denial-of-service-via-link-bracket-parsing

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