How serious is CVE-2026-30838?

This vulnerability has a CVSS score of 5.1 out of 10, classified as MEDIUM severity. Proof-of-concept exploit code is publicly available, making this an active threat.

Is there exploit code available for CVE-2026-30838?

Yes, proof-of-concept exploit code for CVE-2026-30838 is publicly available on GitHub and security research platforms. This increases the risk of active exploitation.

Which products are affected by CVE-2026-30838?

CVE-2026-30838 affects thephpleague commonmark. Check the full CVE details for specific version information.

How do I fix CVE-2026-30838?

To remediate CVE-2026-30838, check for security patches from thephpleague. Apply all available updates and security patches. If no patch is available, implement recommended workarounds or security controls to mitigate the risk.

CVE-2026-30838

Medium

|5.1

Exploit Available

Plain English Summary

AI-powered analysis for quick understanding

This vulnerability allows an attacker to inject malicious HTML, like a script tag, into applications that use a specific Markdown parser to handle user input, potentially leading to cross-site scripting (XSS) attacks. It can be exploited by cleverly inserting whitespace in disallowed HTML tags, and it affects any application relying on the parser's built-in sanitization without additional protections.

Technical Description

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 Vector Analysis

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionRequired

Confidentiality ImpactHigh

Integrity ImpactHigh

Availability ImpactHigh

ScopeChanged

Vector String

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Exploit Resources

Search for proof-of-concept code and exploit modules

GitHub Search Exploit-DB Nuclei Templates Metasploit Vulners

Official References

NIST NVD

Est. Bounty

$690($500-$1K)

Vendor Response

Grade APatched in 4 days

Quick Information

Published

Mar 7, 2026

about 1 month ago

Last Modified

Mar 11, 2026

27 days ago

Vendor

thephpleague

Product

commonmark