CVE-2026-81927
Published:September 15, 2026
Updated:September 22, 2026
Concrete CMS before 9.5.3 contained a stored cross-site scripting vulnerability in SVG file handling. When SVG processing was set to the non-default "Reject files containing potentially harmful elements" mode (concrete.file_manager.images.svg_sanitization.action = reject), uploaded SVGs were checked only against a small built-in blocklist covering the script element and on* event-handler attributes; the broader enshrined/svg-sanitize pass still ran, but its result was discarded, so vectors it would have stripped, such as a javascript: URI in an xlink:href, were stored unmodified and executed when the file was opened directly. A user able to upload files could thereby run arbitrary JavaScript in the browser of any user who viewed the file. The default sanitize mode was not affected. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 1.8 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:A/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Oriol Ortiz for reporting.
Affected Packages
https://github.com/concretecms/concretecms.git (GITHUB):
Affected version(s) >=9.0.0RC1 <9.5.3Fix Suggestion:
Update to version 9.5.3concrete5/core (PHP):
Affected version(s) >=9.0.0RC1 <9.5.3Fix Suggestion:
Update to version 9.5.3Related Resources (2)
Do you need more information?
Contact UsCVSS v4
Base Score:
1.8
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
PRESENT
Privileges Required
HIGH
User Interaction
ACTIVE
Vulnerable System Confidentiality
LOW
Vulnerable System Integrity
LOW
Vulnerable System Availability
NONE
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
3.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
HIGH
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality
LOW
Integrity
LOW
Availability
NONE
Weakness Type (CWE)
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
EPSS
Base Score:
0.17