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.
Scoring
- Severity
- HIGH
- CVSS base score
- 7.3
- CVSS 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
- EPSS probability
- 0.25%
- CWE
- CWE-79
- Published
- 2026-09-14
- Last modified
- 2026-09-15
Affected products
- Concrete CMS Concrete CMS
Weakness type
Related vulnerabilities
- CVE-2026-78252 — Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in GitLab
- CVE-2026-90943 — parallax filament-comments through 3.0.0 Stored XSS via Comment Body
- CVE-2026-90561 — Strapi 4.x through 4.26.2 and 5.x before 5.48.1 Stored XSS via WYSIWYG
- CVE-2026-89256 — AVideo Bookmark Plugin Stored XSS via Chapter Names
- CVE-2026-89255 — AVideo LoginControl Stored XSS via PGP Public Key
- CVE-2026-89254 — AVideo CustomizeUser Stored XSS via field_name Parameter
- CVE-2026-89253 — AVideo Stored XSS via donationLink in watch page button
- CVE-2026-89249 — AVideo YPTWallet Stored XSS via CryptoWallet Configuration