CVE-2026-3242 in Concrete
Summary
by MITRE • 03/04/2026
In Concrete CMS below version 9.4.8, a rogue administrator can add stored XSS via the Switch Language block. 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:N/VI:L/VA:N/SC:N/SI:N/SA:N. Thanks M3dium for reporting.
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Analysis
by VulDB Data Team • 03/06/2026
The vulnerability identified as CVE-2026-3242 represents a significant security flaw in Concrete CMS versions prior to 9.4.8, specifically targeting the Switch Language block functionality. This issue enables a malicious administrator with elevated privileges to inject stored cross-site scripting payloads that persist within the application's database. The vulnerability stems from insufficient input validation and output sanitization mechanisms within the language switching component, creating an attack vector that allows for persistent XSS exploitation. The CVSS v4.0 score of 4.8 indicates a moderate severity threat that requires a high privilege level for exploitation, yet poses substantial risk due to its persistence and potential for lateral movement within the application environment.
The technical implementation of this vulnerability occurs through the Switch Language block's handling of user-provided language parameters and configuration settings. When an attacker with administrator access modifies the block settings or creates new language switch configurations, the application fails to properly sanitize the input data before storing it in the database. This stored XSS vulnerability allows the malicious payload to execute whenever the affected block is rendered on any page, regardless of whether the user has administrative privileges. The vulnerability specifically affects the administrative interface where language switching functionality is configured, making it particularly dangerous as it can be exploited against other administrators or content editors who interact with the affected blocks.
The operational impact of this vulnerability extends beyond simple XSS execution, as it provides attackers with the ability to manipulate the content management system's administrative interface and potentially escalate their privileges. The stored nature of the payload means that the attack persists even after the initial exploitation, allowing for continuous monitoring of administrator sessions or redirection to malicious sites. Attackers could leverage this vulnerability to steal session cookies, redirect users to phishing sites, or inject additional malicious code into the application's environment. The vulnerability's classification under CWE-79 (Cross-site Scripting) and its alignment with ATT&CK technique T1566.001 (Phishing) demonstrates how this flaw can be weaponized for broader social engineering campaigns targeting CMS administrators.
Mitigation strategies for CVE-2026-3242 primarily focus on immediate patching of Concrete CMS installations to version 9.4.8 or later, which includes proper input sanitization and validation mechanisms for the Switch Language block. Organizations should also implement strict access controls and privilege separation within their CMS environments, ensuring that administrative accounts are protected through multi-factor authentication and regular credential rotation. Network-level monitoring should be enhanced to detect suspicious patterns in language configuration changes or unexpected modifications to block settings. Security teams should conduct comprehensive audits of all administrative interfaces and blocks within the CMS to identify similar vulnerabilities, while implementing Content Security Policy headers to provide additional defense-in-depth against XSS attacks. The vulnerability's CVSS scoring reflects its moderate severity but high potential for exploitation within privileged contexts, making proactive remediation essential for maintaining application security.