Cross-Site Scripting Vulnerability in League CommonMark Solution from The PHP League
CVE-2026-105829

5.3MEDIUM

Key Information:

Vendor

ThePHPleague

Status
Commonmark
Vendor
CVE Published:
8 October 2026

What is CVE-2026-105829?

League CommonMark versions prior to 2.10.2 are susceptible to a cross-site scripting vulnerability. This security flaw occurs when users post Markdown, allowing them to circumvent the DisallowedRawHtml extension. By terminating raw HTML with a bare disallowed tag, attackers can embed standalone <script or <iframe tags. Subsequently, they can supply attributes such as src or onload, leading to the execution of stored scripts within the viewers' browsers. This issue poses a significant threat under the default GitHub Flavored Markdown (GFM) settings, potentially allowing attackers to inject malicious content and compromise user data.

References

https://github.com/thephpleague/commonmark/security/advis...
vendor-advisory
https://www.vulncheck.com/advisories/league-commonmark-1....
third-party-advisory

CVSS V4

Score:
5.3
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
Low
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
Unknown

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

4n86rakam1
.