CVE-2026-30838
mediumpriority · track · 24EPSS 0.002 · 13 %ileDEEUUSEPSS · scored 2026-10-27
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.
cvss
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · low–medium · 1.2–6.1
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
The CWE weakness classes this flaw belongs to.
affected products (5)
Products and version ranges known to be affected.
advisories (2)
Vendor and ecosystem advisories describing this.
- WID-SEC-W-2026-1001Snipe-IT: Mehrere Schwachstellen ermöglichen Umgehen von Sicherheitsvorkehrungen und potenziell Cross-Site ScriptingDeutsch2026-04-07csaf · cert_bundDE
Ein Angreifer kann mehrere Schwachstellen in Snipe-IT ausnutzen, um Sicherheitsvorkehrungen zu umgehen, und potenziell um einen Cross-Site Scripting Angriff durchzuführen.
- GHSA-4v6x-c7xx-hw9fCommonMark has DisallowedRawHtml extension bypass via whitespace in HTML tag names2026-03-06ghsa · osvUS
### 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](https://commonmark.thephpleague.com/2.x/security/#additional-filtering))
also known as (3)
Other names and identifiers for this entity.
sources
Which sources assert this record, and when.
references (5)
External citations — patches, advisories, analysis.
- https://access.redhat.com/security/cve/cve-2026-30838cnnvd
- https://github.com/thephpleague/commonmark/releasesPatchcnnvd
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-4v6x-c7xx-hw9fcnnvd
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-4v6x-c7xx-hw9fenisa_euvd
- https://github.com/thephpleague/commonmark/security/advisories/GHSA-4v6x-c7xx-hw9fMitigationVendor Advisorynvd
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