CVE-2025-69251 is a vulnerability classified under CWE-20 (Improper Input Validation) affecting the Unified Data Management (UDM) component of free5GC, an open-source 5G mobile core network implementation. Specifically, in versions up to and including 1.4.1, the UDM's Nudm_UECM service fails to properly sanitize the ueId parameter. Attackers can inject control characters such as the null byte (%00), which leads to internal URL parsing errors within the Go net/url package, manifesting as 'invalid control character' errors. These errors inadvertently expose internal system implementation details through error messages or abnormal responses. Such information disclosure can assist attackers in fingerprinting the service, understanding its internal workings, and potentially identifying further vulnerabilities or misconfigurations. The vulnerability is remotely exploitable over the network without requiring authentication or user interaction, increasing its risk profile. Although the vulnerability does not directly compromise data integrity or availability, the confidentiality impact is high due to information leakage. The free5gc project has addressed this issue in pull request 76, which sanitizes input to prevent control character injection. No alternative workarounds exist at the application level, making patching the definitive mitigation. This vulnerability highlights the importance of rigorous input validation in telecom core network components, which are critical infrastructure elements in 5G deployments.

The primary impact of CVE-2025-69251 is information disclosure through improper input validation leading to internal URL parsing errors. This leakage of system implementation details can aid attackers in service fingerprinting, enabling them to map the network architecture and identify potential attack vectors. For organizations deploying free5GC UDM in their 5G core networks, this vulnerability can facilitate reconnaissance activities by threat actors, including nation-state adversaries and cybercriminals targeting telecom infrastructure. While it does not directly allow unauthorized data modification, code execution, or denial of service, the exposed information can be leveraged in multi-stage attacks, increasing the overall risk. Given the critical role of UDM in subscriber data management and authentication in 5G networks, any compromise or reconnaissance advantage can have cascading effects on network security and user privacy. The vulnerability's remote exploitability without authentication further elevates the threat, especially in environments where the UDM service is exposed or insufficiently segmented. This could lead to targeted attacks against telecom operators, infrastructure providers, and enterprises using open-source 5G core solutions.

1. Apply the official patch from free5gc pull request 76 immediately to all affected UDM deployments to sanitize the ueId parameter and prevent control character injection. 2. Implement strict input validation and sanitization at the network ingress points, including web application firewalls or API gateways, to block malformed or suspicious ueId values before they reach the UDM service. 3. Employ network segmentation and access controls to restrict exposure of the Nudm_UECM service to trusted internal networks only, minimizing the attack surface. 4. Monitor logs and error messages for unusual URL parsing errors or malformed requests indicative of exploitation attempts. 5. Conduct regular security assessments and fuzz testing on telecom core network components to identify similar input validation weaknesses proactively. 6. Coordinate with the free5gc open-source community for timely updates and security advisories to stay ahead of emerging vulnerabilities. 7. Consider deploying runtime application self-protection (RASP) or anomaly detection tools tailored for 5G core network services to detect and block exploitation attempts in real time.