The vulnerability identified as CVE-2025-69251 affects the Unified Data Management (UDM) component of free5GC, an open-source 5G core network implementation. Specifically, versions up to and including 1.4.1 of free5gc UDM improperly validate input for the ueId parameter in the Nudm_UECM service. Attackers can inject control characters such as the null byte (%00), which are not properly sanitized before URL parsing. This leads to internal errors in the net/url package, revealing system implementation details through error messages. Such information disclosure can assist attackers in fingerprinting the service and understanding its internal workings, which may facilitate further targeted attacks. The vulnerability does not require authentication or user interaction and can be exploited remotely over the network. The issue is classified under CWE-20 (Improper Input Validation). Although no direct application-level workaround exists, the free5gc project has addressed the vulnerability in pull request 76, which should be applied to affected deployments to remediate the issue.

The primary impact of CVE-2025-69251 is information disclosure through error messages that reveal internal system details. This can aid attackers in service fingerprinting, enabling them to tailor subsequent attacks more effectively. While the vulnerability does not directly allow code execution or denial of service, the leakage of implementation details can lower the barrier for more severe exploits. Given that free5GC UDM is a critical component in 5G core networks responsible for subscriber data management, attackers gaining reconnaissance information could target these networks to disrupt services or compromise subscriber data. The vulnerability affects all deployments using the Nudm_UECM service of free5GC UDM up to version 1.4.1, potentially impacting telecom operators and infrastructure providers relying on this open-source 5G core solution. The ease of remote exploitation without authentication increases the risk profile, especially in environments where the UDM service is exposed or insufficiently segmented.

To mitigate CVE-2025-69251, organizations should promptly apply the official patch provided in free5gc/udm pull request 76, which properly sanitizes and validates the ueId parameter to prevent control character injection. Network-level protections should be implemented to restrict access to the Nudm_UECM service, limiting exposure to trusted internal networks or VPNs. Deploying Web Application Firewalls (WAFs) or intrusion detection/prevention systems (IDS/IPS) with rules to detect and block suspicious control character sequences in URL parameters can provide additional defense layers. Monitoring logs for URL parsing errors or unusual input patterns can help detect attempted exploitation. As no application-level workaround exists, patching remains the most effective remediation. Additionally, organizations should follow secure coding practices for input validation in custom modifications and keep free5GC components updated to the latest secure versions.