ePA3-Service-OpenSource: Reusing a Nonce, Key Pair in Encryption
CVE-2026-50577 is a high-severity reusing a nonce, key pair in encryption vulnerability in ePA3-Service-OpenSource from fbeta-GmbH, with a CVSS 3.1 base score of 7.4 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected ePA3-Service-OpenSource versions: < 1.3.0. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.51% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of ePA3-Service-OpenSource you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| fbeta-GmbH | ePA3-Service-OpenSource | < 1.3.0 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N. Scored by CNA (github.com).
Official description
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Reusing a Nonce, Key Pair in Encryption
Nonces should be used for the present occasion and only once.
How developers prevent this class of flaw
- Use techniques such as requiring incrementing, time based and/or challenge response to assure uniqueness of nonces.
More Reusing a Nonce, Key Pair in Encryption vulnerabilities (CWE-323)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other references
Other vulnerabilities in ePA3-Service-OpenSource
- 9.1 Critical severity
- 7.5 High severity
Recent Reusing a Nonce, Key Pair in Encryption vulnerabilities
- 7.1 High severity
- 9.1 Critical severity
- 7.5 High severity
- 9.1 Critical severity
- 9.1 Critical severity
- 7.1 High severity
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