CVE-2026-44900: Oviva epa4all-client signature bypass in SignedPublicKeysTrustValidator

Executive brief

The epa4all-client library, used for interacting with electronic patient records, contains a flaw that fails to properly verify digital signatures. This allows an attacker on the same network to bypass security checks and potentially access or modify sensitive health data. The vulnerability effectively disables the trust mechanism intended to ensure that communications are authentic.

Technical details

A signature bypass vulnerability exists in the SignedPublicKeysTrustValidatorImpl.isTrusted() method of the epa4all-client library. The implementation performs certificate chain validation and OCSP checks but discards the boolean return value of the Signature.verify() call. Consequently, the method returns true for any signature that is structurally valid, regardless of whether the cryptographic signature actually matches the data. An attacker on an adjacent network can exploit this to bypass VAU (Vertrauenswürdige Ausführungsumgebung) signature requirements. The issue is addressed in version 1.2.1.

Affected products

• oviva-ag epa4all-client <= 1.2.0

Timeline

• 2026-05-06: disclosed: Initial disclosure by researchers
• 2026-05-08: advisory: GitHub Advisory published
• 2026-05-26: patched: NVD publication date

References

• https://api.github.com/users/snomi
• https://github.com/snomi
• https://api.github.com/users/snomi/gists%7B/gist_id%7D
• https://api.github.com/users/snomi/repos
• https://avatars.githubusercontent.com/u/19928196?v=4
• https://api.github.com/users/snomi/events%7B/privacy%7D