Mistune: XSS via percent-encoded javascript URI bypass in safe_url()
Priority MEDIUM 60CWE-79Published · Updated
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: 3 without a fix
Attack profile from CVSS 3.1 · CNA. 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 3.3.0, HTMLRenderer.safe_url() does not block percent-encoded javascript URIs, allowing attacker-supplied Markdown links or images to bypass URL protections and execute script in rendered HTML. This issue is fixed in version 3.3.0.
Why it matters now
Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00348 28th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Partial mistune (lepture): 3.3.0mistune (PyPI): 3.3.0Red Hat: 3 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 3.3.0 | 3.3.0 | Patch available | CNA |
| — | mistune (PyPI) | before 3.3.0 | 3.3.0 | Patch available | GHSA-8c25-4j27-2rv3 |
- mistune Vendorlepture Affected before 3.3.0 Fixed in 3.3.0 Patch available CNA
- mistune (PyPI) Vendor— Affected before 3.3.0 Fixed in 3.3.0 Patch available GHSA-8c25-4j27-2rv3
Remediation
- Fix · CNA mistune (lepture) Fixed in 3.3.0
- Fix · GHSA-8c25-4j27-2rv3 mistune (PyPI) Fixed in 3.3.0 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 |
| Red Hat OpenShift Container Platform 4 | Affected | No fix yet: Fix deferred |
Not affected: 1 product
- Red Hat Satellite 6
Timeline
- 2026-10-02 Threatist record created from CVE-2026-59923
- 2026-10-03 Alias added: GHSA-8c25-4j27-2rv3
References
More lepture Mistune vulnerabilities
- 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-2026-32774 Mistune Image Directive CSS Injection Vulnerability 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
Sources
- CVE-2026-59923 · CVE Program
- CVE-2026-59923 · NVD
- FIRST EPSS
- GHSA-8c25-4j27-2rv3 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-59923 · Red Hat security data · CC BY 4.0
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