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CVE-2026-81900

Status: AnalyzedHigh (7.3)—

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

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

🎯 ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

XSS almacenado en bloque YouTube (CWE-79) sin escape en atributos HTML. Requiere permisos edit_block pero se ejecuta en navegador de visitantes con contexto de administrador.

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

🛡️ ATT&CK mitigations that cover these techniques

Restrict Web-Based ContentUser TrainingExecution PreventionBehavior Prevention on EndpointDisable or Remove Feature or ProgramApplication Isolation and Sandboxing

Affected technologies (1)

Concretecms — Concrete CMS

CWEs

References

Raw JSON (NVD)

Show
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