CVE-2026-50577 PUBLISHED

ePA 3.x Integration: AES-GCM Nonce Reuse via Frozen VAU Request Counter

Assigner: GitHub_M
Reserved: 04.06.2026 Published: 18.08.2026 Updated: 18.08.2026

ePA 3.x Integration implements the authorization workflow and writes Medical Information Objects to Germany's electronic patient record. Prior to 1.3.0, ePA 3.x Integration leaves request_counter unchanged in app/vau/VAUProtokoll.py while constructing VAU messages. The frozen client request counter causes the server side to reuse AES-GCM nonce and key combinations across responses. A network attacker who collects repeated ciphertexts can recover the XOR of plaintexts and use predictable inner HTTP headers and JSON fields to recover sensitive data, including patient health records. Repeated nonces can also enable recovery of the GHASH authentication key through the Joux forbidden attack, allowing forged AES-GCM messages and injection of malicious responses. The response-counter check also fails to maintain last_response_counter, weakening replay and ordering validation. This issue is fixed in version 1.3.0.

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CVSS Score: 7.4

Product Status

Vendor fbeta-GmbH
Product ePA3-Service-OpenSource
Versions
  • Version < 1.3.0 is affected

References

Problem Types

  • CWE-323: Reusing a Nonce, Key Pair in Encryption CWE