Python-Markdown 3.0 through 3.11.2 Denial of Service via Link Bracket Parsing

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.

Scores

EPSS (exploitation in 30 days)

0.42% · top 63% of all CVEs (7 Nov 2026)

CISA SSVC

Exploitation: poc · Automatable: yes · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.7.

Weakness

• CWE-407: Inefficient Algorithmic Complexity (opens in a new tab)All about CWE-407 and its CVEs

Affected products

• Python-Markdown · Markdown

  • affected 3.0 – ≤ 3.11.2

References (5)

• GitHub Issue #798 (opens in a new tab)issue-tracking
• https://github.com/Python-Markdown/markdown (opens in a new tab)product
• GitHub Issue #1654 (opens in a new tab)issue-trackingexploit
• https://github.com/Python-Markdown/markdown/blob/b41e0aaf1181f1a8cb200cf5a815aad7c0020d23/markdown/inlinepatterns.py#L1155-L1172 (opens in a new tab)technical-description
• VulnCheck Advisory: Python-Markdown 3.0 through 3.11.2 Denial of Service via Link Bracket Parsing (opens in a new tab)third-party-advisory

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2019-25781](https://trackcve.app/badge/CVE-2019-25781.svg)](https://trackcve.app/cve/CVE-2019-25781)

Record last updated 3 Nov 2026, 15:29 UTC.