CVE-2022-23632 is a vulnerability in Traefik, an HTTP reverse proxy and load balancer widely used to manage and route web traffic. The issue pertains to improper certificate validation (CWE-295) in versions prior to 2.6.1. Specifically, when a request uses a fully qualified domain name (FQDN) in the host header, Traefik skips the router-specific TLS configuration and instead falls back to a default TLS configuration. This behavior can cause the TLS configuration applied to a request to differ from the router’s intended TLS settings. The problem is exacerbated when CNAME flattening is enabled: the TLS configuration is selected based on the Server Name Indication (SNI) value, while routing uses the CNAME target, potentially bypassing the expected TLS configuration entirely. This mismatch can lead to the use of incorrect or less secure TLS certificates, undermining the confidentiality and integrity of communications. The vulnerability was patched in Traefik version 2.6.1. While a partial workaround exists by explicitly adding the FQDN to the host rule, no workaround is available if CNAME flattening is enabled, leaving systems vulnerable until patched. No known exploits have been reported in the wild to date.

For European organizations, this vulnerability poses a risk to secure communications managed via Traefik reverse proxies, particularly in environments where TLS configurations are critical for compliance and data protection (e.g., finance, healthcare, government). The improper TLS validation could allow attackers to intercept or manipulate traffic by exploiting the fallback to default or incorrect TLS configurations, potentially enabling man-in-the-middle (MITM) attacks. This could lead to unauthorized data disclosure, session hijacking, or injection of malicious content. Organizations relying on CNAME flattening in DNS configurations are at higher risk, as no workaround exists in this scenario. The impact is significant for multi-tenant or microservices architectures where precise TLS routing is essential. Given Traefik’s popularity in cloud-native and containerized environments, the vulnerability could affect a broad range of services, disrupting availability and trust in secure communications.

The primary mitigation is to upgrade Traefik to version 2.6.1 or later, where the vulnerability is patched. Organizations should audit their Traefik configurations to identify usage of FQDNs in host headers and verify if CNAME flattening is enabled. If upgrading immediately is not feasible, explicitly adding the FQDN to the host rule can serve as a temporary workaround, but only if CNAME flattening is disabled. It is critical to review DNS configurations to avoid reliance on CNAME flattening where possible. Additionally, organizations should implement strict monitoring and logging of TLS handshake failures or anomalies in Traefik logs to detect potential exploitation attempts. Network-level protections such as TLS inspection and anomaly detection can help identify suspicious traffic patterns. Finally, conducting penetration testing focused on TLS routing and certificate validation can help validate the effectiveness of mitigations.