The Node.js web service on VOS (previously Versa FlexVNF) is used for URL-based Zero Touch Provisioning (ZTP) of the VOS appliance and is not required after provisioning is complete. The /decryptTest endpoint of this service is registered in server.js before the session authentication middleware and creates an authenticated session whenever it receives a token that decrypts successfully. Because the key and initialization vector (IV) used for decryption are hardcoded and identical across all VOS appliances, an unauthenticated attacker with network access can compute a valid token, submit it to /decryptTest, and obtain a fully authenticated session without providing any credentials. 

Versa’s security hardening guide for Hubs, Branches, and Controllers recommends disabling the Node.js web service after the initial provisioning of the VOS device. This vulnerability is not exploitable on VOS devices where the Node.js web service has been disabled.