PHP
CVE-2026-30838
MEDIUM
GHSA-4v6x-c7xx-hw9f
Severity by source
AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Lifecycle Timeline
3DescriptionGitHub Advisory
league/commonmark is a PHP Markdown parser. Prior to version 2.8.1, the DisallowedRawHtml extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowed HTML tag name and the closing >. For example, <script\n> would pass through unfiltered and be rendered as a valid HTML tag by browsers. This is a cross-site scripting (XSS) vector for any application that relies on this extension to sanitize untrusted user input. All applications using the DisallowedRawHtml extension to process untrusted markdown are affected. Applications that use a dedicated HTML sanitizer (such as HTML Purifier) on the rendered output are not affected. This issue has been patched in version 2.8.1.
AnalysisAI
The DisallowedRawHtml extension in PHP Commonmark (league/commonmark) versions prior to 2.8.1 can be bypassed by injecting whitespace characters between HTML tag names and closing brackets, allowing malicious scripts to pass sanitization filters and execute in user browsers. Applications relying solely on this extension to sanitize untrusted markdown input are vulnerable to cross-site scripting attacks, though those using additional HTML sanitizers are unaffected. No patch is currently available for affected versions.
Technical ContextAI
Classified as CWE-79 (Cross-site Scripting (XSS)). Affects Commonmark. league/commonmark is a PHP Markdown parser. Prior to version 2.8.1, the DisallowedRawHtml extension can be bypassed by inserting a newline, tab, or other ASCII whitespace character between a disallowed HTML tag name and the closing >. For example, <script\n> would pass through unfiltered and be rendered as a valid HTML tag by browsers. This is a cross-site scripting (XSS) vector for any application that relies on this extension to sanitize untrusted user input. All applications using the Disallo
RemediationAI
Fixed in version 2.8.1.. Implement output encoding and Content Security Policy headers. Restrict network access to the affected service where possible.
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Same weakness CWE-79 – Cross-site Scripting (XSS)
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External POC / Exploit Code
Leaving vuln.today