WS-2026-0049
Published:August 09, 2026
Updated:September 02, 2026
league/commonmark's AttributesExtension left a form feed (U+000C) inside attribute names because PHP's default trim() charlist omits the byte that PCRE's \s matches. Browsers treat U+000C as whitespace between attributes, so a name written as {<FF>onclick="..."} reached the browser as a genuine onclick handler, bypassing both the on* event-handler filter and the allow_unsafe_links protection and yielding cross-site scripting. Fixed in 2.9.1 by trimming attribute names and values with an explicit charlist that includes \x0C.
Affected Packages
https://github.com/thephpleague/commonmark.git (GITHUB):
Affected version(s) >=2.7.0 <2.9.1Fix Suggestion:
Update to version 2.9.1league/commonmark (PHP):
Affected version(s) >=2.7.0 <2.9.1Fix Suggestion:
Update to version 2.9.1Related Resources (2)
Do you need more information?
Contact UsCVSS v4
Base Score:
6.9
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
LOW
Vulnerable System Integrity
LOW
Vulnerable System Availability
NONE
Subsequent System Confidentiality
LOW
Subsequent System Integrity
LOW
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.2
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE