CVE-2026-59928

Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions

State: Published
Severity: 7.5 High
Published: Jul 8, 2026
Updated: Jul 8, 2026
Reserved: Jul 7, 2026

Description

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, a Markdown document containing many repeated or distinct reference-link definitions causes quadratic work in src/mistune/block_parser.py and the ref_links environment dictionary handling, allowing denial of service through CPU exhaustion. This issue is fixed in version 3.3.0.

Scores

CVSS	Score	Vector	Source
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	GitHub_M

Weaknesses

CWE-407 Inefficient Algorithmic Complexity
CWE-1333 Inefficient Regular Expression Complexity

Affected Products

Product	Versions
mistunelepture	< 3.3.0Affected

References

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