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CVE-2026-59928

33
FAUCET Score

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.

First published: Jul 8, 2026Last modified: Jul 8, 2026

Impacted Technologies

VendorProductVersion(s)CPE
< 3.3.0CPE matchmatch criteria
cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.41%
Probability of exploitation in next 30 days
EPSS Percentile
33.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0041 is in the 13th percentile among its peer group of 51,551 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.1 Mastodon, and 0.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (2)

github_advisorypatch availablevia nvd_reference
View patch
pippatch availablevia ghsa
Product: mistuneFixed in: 3.3.0

Vendor Advisories (2)

pipGHSA-ffq3-xpv3-j92qhigh

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

Jul 20, 2026
microsoft2026-Jul/CVE-2026-59928Important

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

Jul 2, 2026

References

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