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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-50577
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-18 17:16:58 UTC
Updated2026-08-18 17:16:58 UTC
DescriptionePA 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.

Risk And Classification

Primary CVSS: v3.1 7.4 HIGH from [email protected]

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

EPSS: 0.003140000 probability, percentile 0.242190000 (date 2026-08-19)

Problem Types: CWE-323 | CWE-323 CWE-323: Reusing a Nonce, Key Pair in Encryption

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.4HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
3.1CNADECLARED7.4HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Fbeta-GmbH EPA3-Service-OpenSource affected < 1.3.0 Not specified

References

ReferenceSourceLinkTags
github.com/fbeta-GmbH/ePA3-Service-OpenSource/commit/85c4c516088c38b9cf2... [email protected] github.com
github.com/fbeta-GmbH/ePA3-Service-OpenSource/releases/tag/1.3.0 [email protected] github.com
www.machinespirits.de/advisory/df27cd [email protected] www.machinespirits.de
github.com/fbeta-GmbH/ePA3-Service-OpenSource/pull/10 [email protected] github.com
github.com/fbeta-GmbH/ePA3-Service-OpenSource/security/advisories/GHSA-v... [email protected] github.com
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