CVE-2026-81900

Concrete CMS before 9.5.3 applied only trim() to the YouTube block's stored width and height values and printed them into iframe HTML attributes without escaping or integer casting, resulting in stored cross-site scripting. A user with edit_block permission could inject an event handler that executed script for visitors rendering the page, acting with administrative privileges where the victim was an administrator. The Concrete CMS security team gave this vulnerability a CVSS v4.0 score of 7.3 with vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N. Thanks sh4d0byss for reporting.

CVSS v3 6.1 MEDIUM

6.1^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 2.7

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact LOW

Integrity Impact LOW

Availability Impact NONE

Scope CHANGED

References

Link	Resource
https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes	Broken Link

Configurations

Configuration 1 (hide)

cpe:2.3:a:concretecms:concrete_cms:*:*:*:*:*:*:*:*

History

16 Sep 2026, 20:47

Type	Values Removed	Values Added
References	~~() https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes -~~	() https://documentation.concretecms.org/developers/introduction/version-history/953-release-notes - Broken Link
CPE		cpe:2.3:a:concretecms:concrete_cms::::::::
CVSS	v2 : ~~unknown~~ v3 : ~~unknown~~	v2 : unknown v3 : 6.1
First Time		Concretecms concrete Cms Concretecms

Information

Published : 2026-09-14 23:18

Updated : 2026-09-16 20:47

NVD link : CVE-2026-81900

Mitre link : CVE-2026-81900

CVE.ORG link : CVE-2026-81900

JSON object : View

Products Affected

concretecms

concrete_cms

CWE

CWE-79

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

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