CVE-2026-59928

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.

CVSS 3.1

7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

0.7% chance of exploitation in the next 30 days; higher than 50% of CVEs (scores of 2026-10-25)

CWEs

CWE-407, CWE-1333

Published

2026-07-08

Modified

2026-10-25

Record from

the NVD, synced 2026-10-25

Affected

• mistune_project:mistune

Packages (OSV)

References

• https://github.com/lepture/mistune/commit/2b04d7ba341c16ac78fe82d3076bdd5c3de87c69
• https://github.com/lepture/mistune/releases/tag/v3.3.0
• https://github.com/lepture/mistune/security/advisories/GHSA-ffq3-xpv3-j92q
• https://github.com/lepture/mistune/security/advisories/GHSA-ffq3-xpv3-j92q

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