TI-2026-32774 Aliases CVE-2026-44899 GHSA-ccfx-mfmx-2fx9

Mistune Image Directive CSS Injection Vulnerability

MEDIUM 60CWE-79Published 2026-05-26 · Updated 2026-05-27

Key facts

Attack vector: Network
Privileges required: None
User interaction: Required
Attack complexity: Low
Impact type: Cross-site scripting
Confidentiality · integrity · availability: Low · Low · None
Fix status: Partial Red Hat: 2 without a fix

Attack profile from CVSS 3.1 · NVD. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-79.

Summary

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, the Image directive plugin validates the :width: and :height: options with a regex compiled as _num_re = re.compile(r"^\d+(?:\.\d*)?"). When the validated value is not a plain integer, render_block_image() inserts it directly into a style="width:...;" or style="height:...;" attribute. Because the value was accepted by the prefix-only regex, any CSS after the leading digits reaches the style= attribute verbatim and without escaping. This vulnerability is fixed in 3.2.1.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00228 13th percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix Partial mistune (lepture): 3.2.1mistune (PyPI): 3.2.1Red Hat: 2 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
lepture	mistune	before 3.2.1	3.2.1	Patch available	CNA
—	mistune (PyPI)	3.2.0 to before 3.2.1	3.2.1	Patch available	GHSA-ccfx-mfmx-2fx9

mistune Vendorlepture Affected before 3.2.1 Fixed in 3.2.1 Patch available CNA
mistune (PyPI) Vendor— Affected 3.2.0 to before 3.2.1 Fixed in 3.2.1 Patch available GHSA-ccfx-mfmx-2fx9

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:mistune_project:mistune::::::::	before 3.2.1	Vulnerable	lepture

cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:* Versions before 3.2.1 Vulnerable ·lepture

Remediation

Fix · CNA mistune (lepture) Fixed in 3.2.1
Fix · GHSA-ccfx-mfmx-2fx9 mistune (PyPI) Fixed in 3.2.1 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Migration Toolkit for Applications 8	Affected	No fix yet: Fix deferred
Red Hat OpenShift AI (RHOAI)	Affected	No fix yet: Fix deferred

Not affected: 2 products

Red Hat OpenShift Container Platform 4
Red Hat Satellite 6

Timeline

2026-10-02 Threatist record created from CVE-2026-44899
2026-10-03 Alias added: GHSA-ccfx-mfmx-2fx9

References

Exploit 1

https://github.com/lepture/mistune/security/advisories/GHSA-ccfx-mfmx-2fx9

Advisory 1

https://nvd.nist.gov/vuln/detail/CVE-2026-44899

Other 2

TI-2026-42736 Mistune block_parser: quadratic-time parsing on long lists of repeated reference-link definitions CVSS 3.1HIGH 7.5
TI-2026-42730 Regular expression denial of service in lepture mistune CVSS 3.1HIGH 7.5
TI-2026-42731 Mistune: XSS via percent-encoded javascript URI bypass in safe_url() CVSS 3.1MEDIUM 6.1
TI-2026-32773 Mistune TOC Anchor Injection XSS CVSS 3.1MEDIUM 6.1
TI-2026-32595 Mistune Math Plugin XSS Escape Bypass CVSS 3.1MEDIUM 6.1
TI-2026-42738 Insufficient verification of data authenticity in lepture mistune CVSS 3.1MEDIUM 4.3

See all 16 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences