CVE-2026-40248: free5gc UDR improper path validation allows unauthenticated creation and modification of Traffic Influence Subscriptions

Vulnerability summary

CVE-2026-40248 is a high (CVSS 8.7) Improper Authorization vulnerability in free5gc. EPSS estimates a 0.50% chance of exploitation in the next 30 days, higher than 42.1% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 16-04-2026
   PublishedVulnerability first disclosed.
2. 20-04-2026
   Last modifiedVulnerability information updated.

Description

free5GC is an open-source implementation of the 5G core network. In versions 4.2.1 and below of the UDR service, the handler for creating or updating Traffic Influence Subscriptions checks whether the influenceId path segment equals subs-to-notify, but does not return after sending the HTTP 404 response when validation fails. Execution continues and the subscription is created or overwritten regardless. An unauthenticated attacker with access to the 5G Service Based Interface can create or overwrite arbitrary Traffic Influence Subscriptions, including injecting attacker-controlled notificationUri values and arbitrary SUPIs, by supplying any value for the influenceId path segment. A patched version was not available at the time of publication.

• CWE-285Improper AuthorizationThe product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action.
• CWE-636Not Failing Securely ('Failing Open')When the product encounters an error condition or failure, its design requires it to fall back to a state that is less secure than other options that are available, such as selecting the weakest encryption algorithm or using the most permissive access control restrictions.