Concrete CMS 9.4.3 Vulnerable to Stored XSS Attack (CVE Pending)

Concrete CMS 9.4.3 Affected by Stored Cross-Site Scripting (XSS) Vulnerability

Security researchers have identified a stored cross-site scripting (XSS) vulnerability in Concrete CMS version 9.4.3, which could allow attackers to inject and execute malicious scripts in the context of a victim's browser session. The flaw was disclosed via Exploit Database but has not yet been assigned a CVE ID at the time of reporting.

Technical Details

The vulnerability stems from insufficient input validation and output encoding in Concrete CMS, enabling attackers to embed arbitrary JavaScript code within web pages. When a user accesses a compromised page, the malicious script executes in their browser, potentially leading to:

• Session hijacking (theft of authentication cookies)
• Account takeover (via credential harvesting or forced actions)
• Defacement or redirection to phishing/malware sites
• Propagation of further attacks (e.g., exploiting browser-based vulnerabilities)

The exploit requires authenticated access to the CMS, though researchers note that low-privilege roles (e.g., contributors) may suffice for exploitation. Details of the specific attack vector remain limited pending a vendor patch.

Impact Analysis

Stored XSS vulnerabilities are particularly severe due to their persistent nature—malicious scripts remain embedded in the application until manually removed. Organizations using Concrete CMS 9.4.3 face risks including:

• Data breaches via stolen session tokens or credentials.
• Reputation damage from defaced websites or unauthorized content.
• Compliance violations (e.g., GDPR, PCI DSS) if user data is compromised.

Mitigation and Recommendations

While a patch is not yet available, security teams should implement the following measures:

1. Restrict CMS Access: Limit user roles to the principle of least privilege, particularly for contributors and editors.
2. Input Sanitization: Deploy a web application firewall (WAF) to filter malicious payloads targeting XSS vectors.
3. Monitoring: Audit CMS logs for unusual activity, such as unexpected script injections or unauthorized content changes.
4. User Training: Educate staff on recognizing phishing attempts that could exploit XSS flaws to harvest credentials.
5. Upgrade Path: Monitor the Concrete CMS security advisories for official patches and apply updates immediately upon release.

Security professionals are advised to review the Exploit-DB proof-of-concept for technical indicators of compromise (IoCs). Further updates will be provided as the vendor releases a fix.