CVE-2025-3984 is a critical code injection vulnerability identified in Apereo CAS version 5.2.6, specifically within the saveService function of the RegisteredServiceSimpleFormController.java file. This function is part of the Groovy Code Handler component used in the CAS management web application. The vulnerability allows an attacker to remotely inject and execute arbitrary code by manipulating inputs processed by the saveService function. However, the attack complexity is high, indicating that exploitation requires significant effort, expertise, or specific conditions. The vulnerability does not require user interaction but does require low-level privileges (PR:L) to exploit, and the attack vector is network-based (AV:N). The CVSS 4.0 score is 2.3, reflecting a low severity rating due to the high attack complexity and limited impact on confidentiality, integrity, and availability. The vulnerability affects only version 5.2.6 of Apereo CAS, a widely used open-source Central Authentication Service platform for single sign-on (SSO) in enterprise environments. The vendor has not responded to the disclosure, and no patches or mitigations have been officially released. No known exploits are currently active in the wild, but public disclosure increases the risk of future exploitation attempts. The vulnerability impacts the integrity and availability of the CAS service, potentially allowing attackers to execute unauthorized code, which could lead to unauthorized access or service disruption if successfully exploited.

For European organizations, the impact of this vulnerability depends on the extent of Apereo CAS deployment within their IT infrastructure. CAS is commonly used in academic institutions, government agencies, and enterprises for authentication and SSO. Successful exploitation could allow attackers to execute arbitrary code remotely, potentially compromising authentication services, leading to unauthorized access to sensitive systems and data. This could undermine trust in identity management systems and disrupt business operations. However, the high attack complexity and requirement for low privileges reduce the likelihood of widespread exploitation. Organizations relying heavily on CAS for critical authentication services could face risks to service availability and integrity, potentially affecting user access and data confidentiality indirectly. The lack of vendor response and absence of patches increases the urgency for organizations to implement compensating controls. Given the public disclosure, targeted attacks against European institutions using CAS 5.2.6 could emerge, especially in sectors with high-value data or critical infrastructure.

1. Immediate upgrade: Organizations should upgrade Apereo CAS to a later, patched version once available. In the absence of an official patch, consider upgrading to a newer major version of CAS that does not contain this vulnerability. 2. Restrict access: Limit network access to the CAS management web application to trusted administrative networks and IP addresses to reduce exposure to remote attacks. 3. Implement strict input validation: Review and harden input validation and sanitization in the CAS management interface, particularly around service registration forms, to mitigate injection risks. 4. Monitor logs: Enable detailed logging and monitor for suspicious activities related to the saveService function or unusual Groovy script executions. 5. Use Web Application Firewalls (WAF): Deploy WAF rules to detect and block attempts to exploit code injection patterns targeting the CAS management endpoints. 6. Apply the principle of least privilege: Ensure that accounts with access to CAS management have minimal privileges necessary and enforce strong authentication controls. 7. Network segmentation: Isolate CAS management interfaces from general user networks to reduce the attack surface. 8. Incident response readiness: Prepare to respond quickly to any signs of exploitation, including isolating affected systems and conducting forensic analysis.