GHSA-4v6x-c7xx-hw9f

Suggest an improvement
Source
https://github.com/advisories/GHSA-4v6x-c7xx-hw9f
Import Source
https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/03/GHSA-4v6x-c7xx-hw9f/GHSA-4v6x-c7xx-hw9f.json
JSON Data
https://api.test.osv.dev/v1/vulns/GHSA-4v6x-c7xx-hw9f
Aliases
Published
2026-03-06T23:27:03Z
Modified
2026-03-20T21:35:08Z
Severity
  • 5.1 (Medium) CVSS_V4 - CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N/SC:L/SI:L/SA:N CVSS Calculator
Summary
CommonMark has DisallowedRawHtml extension bypass via whitespace in HTML tag names
Details

Impact

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.

Patches

Fixed in 2.8.1. The regex character class [ \/>] was changed to [\s\/>] to match all whitespace characters that browsers accept as valid tag name terminators.

Workarounds

  • Set the html_input configuration option to 'escape' or 'strip' to disable all raw HTML, though this is a broader restriction than the DisallowedRawHtml extension provides.
  • Pass the rendered HTML through a dedicated HTML sanitizer before serving it to users (always recommended)
Database specific 
{
    "cwe_ids":  [
        "CWE-79"
    ],
    "github_reviewed":  true,
    "github_reviewed_at":  "2026-03-06T23:27:03Z",
    "nvd_published_at":  "2026-03-07T16:15:56Z",
    "severity":  "MODERATE"
}
References

Affected packages

Packagist / league/commonmark

Package

Name
league/commonmark
Purl
pkg:composer/league/commonmark

Affected ranges

Type
ECOSYSTEM
Events
Introduced
2.0.0
Fixed
2.8.1

Affected versions

2.*
2.0.0
2.0.1
2.0.2
2.0.3
2.0.4
2.1.0
2.1.1
2.1.2
2.1.3
2.2.0
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.3.0
2.3.1
2.3.2
2.3.3
2.3.4
2.3.5
2.3.6
2.3.7
2.3.8
2.3.9
2.4.0
2.4.1
2.4.2
2.4.3
2.4.4
2.5.0
2.5.1
2.5.2
2.5.3
2.6.0
2.6.1
2.6.2
2.7.0
2.7.1
2.8.0

Database specific

last_known_affected_version_range 
"<= 2.8.0"
source 
"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/03/GHSA-4v6x-c7xx-hw9f/GHSA-4v6x-c7xx-hw9f.json"