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CVE-2025-8571: Concrete CMS 9 through 9.4.2 and below 8.5.21 is vulnerable to Reflected Cross-Site Scripting (XSS) in Conversation Messages Dashboard Page

• Severity: medium (CVSS 4.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-08-05 · updated 2026-06-17
• Weakness: CWE-20

Description

Concrete CMS 9 to 9.4.2 and versions below 8.5.21 are vulnerable to Reflected Cross-Site Scripting (XSS) in the Conversation Messages Dashboard Page. Unsanitized input could cause theft of session cookies or tokens, defacement of web content, redirection to malicious sites, and (if victim is an admin), the execution of unauthorized actions. The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 4.8 with vector CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks Fortbridge https://fortbridge.co.uk/  for performing a penetration test and vulnerability assessment on Concrete CMS and reporting this issue.

Affected products

• Concrete CMS: before 8.5.21; from 9.0 before 9.4.3 — fixed in 8.5.21, 9.4.3

How to fix

Upgrade to a fixed version: Concrete CMS 8.5.21, 9.4.3. Check the vendor advisory for mitigations.

References

• https://documentation.concretecms.org/9-x/developers/introduction/version-history/943-release-notes
• https://documentation.concretecms.org/developers/introduction/version-history/8521-release-notes
• https://www.concretecms.org/download

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