CVE-2026-81900
Concrete CMS before 9.5.3 is vulnerable to Stored XSS in the YouTube block (vWidth/vHeight)
- State
- Published
- Severity
- 7.3 High
- Published
- Sep 14, 2026
- Updated
- Sep 15, 2026
- Reserved
- Aug 27, 2026
Description
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 7.3 High | 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 | ConcreteCMS |
Weaknesses
- CWE-79 Improper Neutralization of Input During Web Page Generation
Affected Products
| Product | Versions |
|---|---|
Concrete CMSConcrete CMS |
|
References
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