epa4all-client Improper Verification of Cryptographic Signature Vulnerability (CVE-2026-45575)

The epa4all-client is vulnerable to a man-in-the-middle (MITM) attack (CVE-2026-45575) due to improper verification of cryptographic signatures. An attacker positioned within the TI network, capable of intercepting and modifying TLS traffic between the client and the Identity Provider (IDP), can substitute the legitimate discovery document with a forged one. This forged document redirects the uri_puk_idp_enc and uri_puk_idp_sig parameters to attacker-controlled URLs. This vulnerability affects versions of com.oviva.telematik:epa4all-client prior to 1.2.2. Successful exploitation allows the attacker to steal the SMC-B-signed challenge response, enabling unauthorized access.

Attack Chain

1. The attacker performs a MITM attack on the TLS connection between the epa4all-client and the IDP within the TI network.
2. The attacker intercepts the legitimate discovery document transmitted from the IDP to the client.
3. The attacker substitutes the legitimate discovery document with a forged document crafted to redirect traffic to attacker-controlled endpoints.
4. The forged discovery document redirects uri_puk_idp_enc and uri_puk_idp_sig to attacker-controlled URLs.
5. The epa4all-client, trusting the forged document, encrypts the SMC-B-signed challenge response using the attacker’s encryption key.
6. The client then POSTs the encrypted, signed authentication material to the attacker’s designated authentication endpoint.
7. The attacker captures the signed authentication material from the POST request.
8. The attacker uses the captured authentication material to gain unauthorized access to protected resources or impersonate the user.

Impact

Successful exploitation of CVE-2026-45575 allows an attacker to capture the SMC-B-signed challenge response, enabling unauthorized access to sensitive healthcare data or services within the Telematikinfrastruktur (TI) network. This could lead to data breaches, compliance violations, and potential misuse of patient information. The vulnerability impacts all deployments of com.oviva.telematik:epa4all-client versions prior to 1.2.2 within the TI network where a MITM attack is feasible.

Recommendation

• Upgrade com.oviva.telematik:epa4all-client to version 1.2.2 or later to incorporate the fix for CVE-2026-45575.
• Implement network monitoring to detect suspicious TLS traffic patterns indicative of MITM attacks within the TI network.
• Monitor network connections for connections to unusual or unexpected external URLs as a result of a forged discovery document.
• Implement the network connection rule to monitor for connections to external IP addresses or domains, as this could indicate a forged discovery document has been used.