CVE-2026-59928
Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions
7.5
HIGH
CVSS 3.1
EPSS 0.37%
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.
How to fix CVE-2026-59928
To remediate CVE-2026-59928, upgrade the affected package to a fixed version below.
- —upgrade to 3.3.0 or later
Is CVE-2026-59928 being exploited?
Low — EPSS is 0.4%, meaning exploitation activity has not been observed at scale.
Affected packages (1)
- from 0, < 3.3.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |