Skip to main content

Mistune CVE-2026-59923

| EUVDEUVD-2026-42331 MEDIUM
Cross-site Scripting (XSS) (CWE-79)
2026-07-08 GitHub_M GHSA-8c25-4j27-2rv3 PYSEC-2026-2211
XSS Python Red Hat Suse Mistune Lepture
6.1
CVSS 3.1 · Vendor: GitHub_M
Share

Severity by source

Vendor (GitHub_M) PRIMARY
6.1 MEDIUM
AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
vuln.today AI
6.1 MEDIUM

Network-reachable with no privileges; UI:R because victim must interact with link; S:C because script executes in victim browser context separate from server.

3.1 AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
SUSE
5.4 MEDIUM
AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
Red Hat
6.1 MEDIUM
qualitative

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

Lifecycle Timeline

2
Patch available
Jul 08, 2026 - 18:02 EUVD
Analysis Generated
Jul 08, 2026 - 17:12 vuln.today

Blast Radius

ecosystem impact
† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth
  • 1 pypi packages depend on mistune (1 direct, 0 indirect)

Ecosystem-wide dependent count for version 3.3.0.

DescriptionCVE.org

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.

AnalysisAI

Cross-site scripting in Mistune Python Markdown parser (all versions before 3.3.0) allows attacker-controlled Markdown content containing percent-encoded javascript: URIs to bypass the HTMLRenderer.safe_url() URL sanitization filter and execute arbitrary script in victim browsers. The bypass works because safe_url() checks the raw string without first decoding percent-encoded characters, so schemes like %6Aavascript: or %6aVaScRiPt: evade detection while remaining valid to browsers. Any web application that renders user-supplied or attacker-influenced Markdown through Mistune and serves the output to other users is exposed. No public exploit or CISA KEV listing has been identified at time of analysis.

Technical ContextAI

Mistune (CPE: cpe:2.3:a:lepture:mistune:*:*:*:*:*:*:*:*) is a widely-used Python Markdown parsing library that supports rendering to HTML with optional sanitization features. Its HTMLRenderer class includes a safe_url() method intended to reject dangerous URL schemes, particularly javascript:, before including them in rendered anchor tags and image src attributes. The root cause (CWE-79: Improper Neutralization of Input During Web Page Generation) is that safe_url() performs scheme detection on the literal input string without first applying percent-decoding. RFC 3986 percent-encoding is fully normalized by browsers before URL scheme dispatch, so %6A or any case-variant encoding of the letter 'j' suffices to produce a valid javascript: URI that browsers will execute while the raw string passes Mistune's allowlist check. This class of bypass has appeared repeatedly in URL sanitizers that operate pre-decode.

RemediationAI

Upgrade Mistune to version 3.3.0, which is the vendor-released patch per the GitHub release at https://github.com/lepture/mistune/releases/tag/v3.3.0 and the corresponding fix commit at https://github.com/lepture/mistune/commit/c7101fcbb6e8790e8e39157c5ca2238fc6dd6cbc. If an immediate upgrade is not possible, the primary compensating control is to apply a secondary URL sanitization step after Mistune rendering - either via a dedicated HTML sanitization library (such as bleach or nh3 for Python) that explicitly allowlists safe URL schemes after percent-decoding, or by stripping anchor href and image src attributes from rendered output entirely when user-supplied content is involved. Note that disabling Mistune's built-in safe_url() check without replacement provides no protection. Wrapping the rendered HTML in a sandboxed iframe (sandbox attribute without allow-scripts) limits script execution but constrains page functionality and does not address the underlying issue.

More in Python

View all
CVE-2025-24016 CRITICAL POC
9.9 Feb 10

Wazuh SIEM platform versions 4.4.0 through 4.9.0 contain an unsafe deserialization vulnerability in the DistributedAPI t
CVE-2025-27520 CRITICAL POC
9.8 Apr 04

BentoML version 1.4.2 and earlier contains an unauthenticated remote code execution vulnerability through insecure deser
CVE-2025-2945 CRITICAL POC
9.9 Apr 03

pgAdmin 4 contains critical remote code execution vulnerabilities in the Query Tool download and Cloud Deployment endpoi
CVE-2013-5093 MEDIUM POC
6.8 Sep 27

The renderLocalView function in render/views.py in graphite-web in Graphite 0.9.5 through 0.9.10 uses the pickle Python

CVE-2025-32375 CRITICAL POC
9.8 Apr 09

BentoML is a Python library for building online serving systems optimized for AI apps and model inference. Rated critica
CVE-2014-0224 HIGH POC
7.4 Jun 05

OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before 1.0.1h does not properly restrict processing of ChangeCiph
CVE-2024-21644 HIGH POC
7.5 Jan 08

pyLoad download manager version prior to 0.5.0b3.dev77 exposes the Flask SECRET_KEY through an unauthenticated endpoint.
CVE-2026-33017 CRITICAL POC
9.3 Mar 17

Langflow (a visual LLM pipeline builder) contains a critical unauthenticated code execution vulnerability (CVE-2026-3301
CVE-2017-9462 HIGH POC
8.8 Jun 06

In Mercurial before 4.1.3, "hg serve --stdio" allows remote authenticated users to launch the Python debugger, and conse
CVE-2026-49869 CRITICAL POC
10.0 Jun 26

Unauthenticated remote code execution affects Kestra OSS (the open-source event-driven orchestration platform) prior to

CVE-2026-39987 CRITICAL POC
9.3 Apr 08

Unauthenticated remote code execution in Marimo ≤0.20.4 allows attackers to execute arbitrary system commands via the `/
CVE-2024-21645 MEDIUM POC
5.3 Jan 08

pyLoad is the free and open-source Download Manager written in pure Python. Rated medium severity (CVSS 5.3), this vulne

Same weakness CWE-79 – Cross-site Scripting (XSS)

View all
CVE-2020-3580 MEDIUM POC
6.1
CVE-2013-7389 MEDIUM POC
4.3
CVE-2021-25299 MEDIUM POC
6.1
CVE-2014-2120 MEDIUM
6.1
CVE-2023-40000 HIGH POC
8.3
CVE-2016-8581 MEDIUM POC
6.1
CVE-2013-5223 MEDIUM POC
5.4
CVE-2025-52367 MEDIUM POC
5.4

Same technique XSS

View all
CVE-2017-9248 CRITICAL POC
9.8
CVE-2020-3580 MEDIUM POC
6.1
CVE-2013-1710 CRITICAL POC
10.0
CVE-2013-7389 MEDIUM POC
4.3
CVE-2021-25299 MEDIUM POC
6.1
CVE-2014-2120 MEDIUM
6.1
CVE-2023-40000 HIGH POC
8.3
CVE-2024-52875 HIGH POC
8.8

Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Server 16.0 SUSE Linux Enterprise Server for SAP applications 16.0 Fixed
openSUSE Leap 16.0 Fixed
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected
SUSE Linux Enterprise Module for Package Hub 15 SP7 Not-Affected

Share

CVE-2026-59923 vulnerability details – vuln.today
Back

This site uses cookies essential for authentication and security. No tracking or analytics cookies are used. Privacy Policy