The vulnerability in the free5GC Unified Data Management (UDM) service allows remote attackers to inject control characters such as %00 into the supi parameter. This triggers internal URL parsing errors, causing the application to expose system‑level error details that can be leveraged for service fingerprinting. The flaw is a classic instance of poor input validation (CWE‑20).

All free5GC deployments running UDM versions up to and including 1.4.1 are affected, as the issue originates in the Nudm_UEAU service implementation. To mitigate, use a version of UDM newer than 1.4.1 or apply the referenced patch.

The CVSS base score of 6.6 indicates moderate severity, while the EPSS score of less than 1% suggests a very low probability of exploitation in the wild. The vulnerability is not listed in the CISA KEV catalog, reinforcing that it is currently low risk. The attack vector is likely remote, requiring an attacker to send a crafted HTTP request to the UDM UEAU endpoint to trigger the error and gain exposed details.