What is CVE-2026-59928?

CVE-2026-59928 is a high-severity vulnerability in Lepture Mistune, classified under Inefficient Algorithmic Complexity. CVSS score: 7.5/10. Published 2026-07-08.

How severe is CVE-2026-59928?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Lepture Mistune

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.

Published 2026-07-08 · last modified 2026-07-09.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.007 (49.6th percentile), scored 2026-10-09.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 50th percentile — 49.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.007 · newest: 0.007 · change: 0.000

Affected products

Lepture Mistune — versions < 3.3.0
Mistune Project

Weakness classification (CWE)

References

github.com/lepture/mistune/security/advisories/GHSA-ffq3-xpv3-j92q (Exploit, Third Party Advisory)
github.com/lepture/mistune/commit/2b04d7ba341c16ac78fe82d3076bdd5c3de87c69 (Patch)
github.com/lepture/mistune/releases/tag/v3.3.0 (Release Notes)

Frequently asked questions

What is CVE-2026-59928?: CVE-2026-59928 is a high-severity vulnerability in Lepture Mistune, classified under Inefficient Algorithmic Complexity. CVSS score: 7.5/10. Published 2026-07-08.
How severe is CVE-2026-59928?: High severity. CVSS v3 base score is 7.5 out of 10.