epa4all-client: Improper Verification of Cryptographic Signature

epa4all-client is the Java Client for epa4all / ePA 3.0 in the Telematik Infrastruktur. Prior to 1.2.2, an attacker who can MITM the TLS connection between the client and the IDP (within the TI network) can substitute a forged discovery document. The forged document redirects uri_puk_idp_enc and uri_puk_idp_sig to attacker-controlled URLs. The client then encrypts the SMC-B-signed challenge response to the attacker's encryption key and POSTs it to the attacker's auth endpoint. This captures the signed authentication material. This vulnerability is fixed in 1.2.2.