Stored XSS via unescaped iframe dimensions
Published Sep 14, 2026 · Updated Sep 14, 2026
Stored XSS in the YouTube block in Concrete CMS before 9.5.3 allows remote authenticated users to execute script in visitors' browsers. The block view applies trim() to stored vWidth and vHeight values, then emits them into iframe attributes without escaping or integer conversion. A user with edit_block permission must store a crafted event handler; it runs when a visitor renders the page and inherits an administrator's browser privileges when that visitor is an administrator.
Summary
What happened
Stored XSS in the YouTube block in Concrete CMS before 9.5.3 allows remote authenticated users to execute script in visitors' browsers. The block view applies trim() to stored vWidth and vHeight values, then emits them into iframe attributes without escaping or integer conversion. A user with edit_block permission must store a crafted event handler; it runs when a visitor renders the page and inherits an administrator's browser privileges when that visitor is an administrator.
The record
- CVE
- CVE-2026-81900
- Published
- Sep 14, 2026
- Updated
- Sep 14, 2026
- Vendor
- Concrete CMS
- Product
- Concrete CMS
- Classifications
- T1059.007
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Sep 14, 2026CVE publishedPublication date reported by the CVE source.
- Sep 14, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=5.0.0 <=9.5.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo