GHSA-QFRW-5RXM-MHH2 Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes that historically chain to `javascript:` execution

Summary Type: URL-scheme allowlist gap. The safeurl filter only blocks the four schemes javascript:, vbscript:, file:, data:. Several other schemes are accepted into rendered and tags despite being known XSS vectors in legacy or chain-handling browsers. The same gap applies to direct links,...

Cross-site Scripting (XSS)

Overview Affected versions of this package are vulnerable to Cross-site Scripting XSS via the safeurl process. An attacker can inject malicious URLs into rendered href and src attributes by crafting links that use legacy or chained schemes, potentially leading to script execution in affected user...

CVE-2026-59929

Mistune is a Python Markdown parser. CVE-2026-59929 affects the safe_url filter in src/mistune/renderers/html.py prior to version 3.3.0, which blocks only javascript:, vbscript:, file:, and data: schemes. This allowed legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha...

CVE-2026-59929 Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes that historically chain to `javascript:` execution

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safeurl filter in src/mistune/renderers/html.py blocks only javascript:, vbscript:, file:, and data: schemes, allowing legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:...

CVE-2026-59929 Mistune renderers/html.safe_url: HARMFUL_PROTOCOLS list misses legacy and chained schemes that historically chain to `javascript:` execution

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.3.0, the safeurl filter in src/mistune/renderers/html.py blocks only javascript:, vbscript:, file:, and data: schemes, allowing legacy or chained schemes such as feed:, view-source:, jar:, livescript:, mocha:, ms-its:, mk:...