CVE-2025-3986 is a vulnerability identified in Apereo CAS version 5.2.6, specifically within the file CasConfigurationMetadataServerController.java. The issue arises from inefficient regular expression complexity triggered by manipulation of the 'Name' argument. This vulnerability can be exploited remotely without requiring authentication or user interaction, making it accessible to unauthenticated attackers over the network. The inefficient regex leads to excessive CPU consumption when processing crafted input, resulting in a Denial of Service (DoS) condition by exhausting server resources. The vulnerability has a CVSS 4.0 base score of 5.3, indicating a medium severity level. The attack vector is network-based with low attack complexity and no privileges or user interaction needed. The scope is limited to the affected CAS server instance, with a low impact on confidentiality and integrity but a potential impact on availability due to resource exhaustion. The vendor has not responded to the disclosure, and no patches are currently available. Although no known exploits are reported in the wild, public disclosure increases the risk of exploitation attempts. Apereo CAS is an open-source Central Authentication Service widely used for single sign-on (SSO) in academic institutions and enterprises, making this vulnerability relevant for organizations relying on CAS 5.2.6 for authentication services.

For European organizations using Apereo CAS 5.2.6, this vulnerability poses a risk primarily to service availability. Exploitation could lead to denial of service, disrupting authentication workflows and potentially causing downtime for critical applications relying on CAS for SSO. This could impact universities, research institutions, and enterprises that depend on CAS for secure access management. While confidentiality and integrity are not directly compromised, the unavailability of authentication services can have cascading effects on business operations and user productivity. Organizations with high dependency on CAS for identity federation and access control may face operational disruptions and increased support costs. Given the lack of vendor response and patches, the window for mitigation is limited, increasing exposure until a fix or workaround is implemented.

1. Immediate mitigation should focus on network-level protections such as rate limiting and web application firewalls (WAFs) to detect and block anomalous requests targeting the vulnerable endpoint, especially those with suspicious 'Name' parameter values. 2. Monitor CAS server logs for unusual spikes in CPU usage or repeated requests to the CasConfigurationMetadataServerController endpoint. 3. If feasible, temporarily disable or restrict access to the affected metadata server controller endpoint until a patch is available. 4. Consider deploying CAS behind reverse proxies that can perform input validation or regex complexity checks to filter malicious payloads. 5. Engage with the Apereo community or maintainers to track patch releases or security advisories. 6. Plan for an upgrade to a patched version once available, or consider alternative authentication solutions if immediate patching is not possible. 7. Implement robust incident response procedures to quickly identify and mitigate DoS attempts targeting authentication infrastructure.