Oviva epa4all-client
VAU Signature Verification Bypass
In SignedPublicKeysTrustValidatorImpl.isTrusted(), the ECDSA verification of the VAU server's signed public keys discards the boolean return value of Signature.verify(). The method falls through to return true regardless of whether the signature is valid, allowing a network attacker to substitute their own keys into the VAU handshake.
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Description
The bug was introduced in the initial commit of the trust validator and remained in every published release of epa4all-client. Java's Signature.verify() returns false for an invalid signature without throwing, so the unused return value masks the failure. The same codebase contains a correct use of the pattern in another verifier.
Impact
- A network attacker positioned between an ePA client and the ePA backend can substitute their own ECDH and Kyber public keys into the VAU handshake. The client derives session keys from the attacker's keys, granting full plaintext access to ePA traffic, including document writes, document reads, and authorization flows.
Mitigation
Update to the next release of epa4all-client after 1.1.1 (incorporating pull request #34). The fix returns the boolean result of Signature.verify() instead of discarding it.
References
How We Can Help
Who We Are
The security researchers behind this advisory.
Dr. rer. nat. Simon Weber
Senior Pentester & MedSec Researcher
I evaluate your SaMD with the same industry-defining security insight I contributed to the BAK MV for the revision of the B3S standard.
- PhD on Hospital Cybersecurity
- Critical vulnerabilities found in hospital systems
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Dipl.-Inf. Volker Schönefeld
Senior Application Security Expert
As a former CTO and developer turned pentester, I work alongside your team to uncover vulnerabilities and find solutions that fit your architecture.
- 20+ years as CTO, 50M+ app downloads
- Architected and secured large-scale IoT fleets
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