CVE-2023-35941 in Envoy
Summary
by MITRE • 07/25/2023
Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12, a malicious client is able to construct credentials with permanent validity in some specific scenarios. This is caused by the some rare scenarios in which HMAC payload can be always valid in OAuth2 filter's check. Versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12 have a fix for this issue. As a workaround, avoid wildcards/prefix domain wildcards in the host's domain configuration.
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Analysis
by VulDB Data Team • 08/18/2023
The vulnerability identified as CVE-2023-35941 affects Envoy, a widely-used open source edge and service proxy designed for cloud-native applications. This security flaw represents a critical authentication bypass issue that undermines the integrity of OAuth2 authentication mechanisms within the proxy. The vulnerability exists in versions prior to 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12, creating a persistent security risk for organizations relying on Envoy for their service mesh and API gateway implementations. The flaw specifically targets the OAuth2 filter's validation process, allowing malicious actors to exploit rare edge cases in HMAC payload validation to construct credentials with permanent validity.
The technical root cause of this vulnerability lies in the specific scenarios where HMAC payload validation fails to properly enforce time-based expiration checks within the OAuth2 filter component. This creates a condition where certain maliciously crafted authentication requests can bypass normal validation procedures and be accepted as valid indefinitely. The vulnerability manifests through the HMAC (Hash-based Message Authentication Code) implementation within the OAuth2 filter, where the validation logic fails to properly verify the temporal aspects of authentication tokens. This represents a weakness in the cryptographic validation process that should normally ensure token freshness and prevent replay attacks. The flaw operates under specific conditions that are not commonly encountered, making it particularly dangerous as it can be exploited without obvious detection mechanisms.
The operational impact of CVE-2023-35941 extends beyond simple authentication bypass to potentially enable unauthorized access to protected services and resources within cloud-native environments. Attackers exploiting this vulnerability could gain persistent access to backend services that rely on Envoy for OAuth2 authentication, leading to data breaches, service disruption, and potential lateral movement within network infrastructures. The implications are particularly severe for organizations using Envoy as a core component of their service mesh architecture, where this vulnerability could compromise the entire authentication ecosystem. The permanent validity of constructed credentials means that once exploited, the impact could persist until the proxy is restarted or updated, creating extended windows of opportunity for malicious actors to maintain unauthorized access. This vulnerability directly violates security principles established in standards such as CWE-284, which addresses improper access control, and aligns with ATT&CK technique T1078 for valid accounts, as it enables unauthorized access through manipulated authentication tokens.
Organizations affected by this vulnerability should immediately implement the recommended remediation measures, with the most effective approach being the upgrade to patched versions of Envoy. The workaround of avoiding wildcards and prefix domain wildcards in host domain configuration provides temporary mitigation but does not fully address the underlying issue. Security teams should also conduct comprehensive audits of their Envoy configurations to identify any instances where the vulnerable OAuth2 filter components are actively deployed. Additionally, monitoring should be enhanced to detect unusual authentication patterns that might indicate exploitation attempts. The vulnerability underscores the critical importance of maintaining up-to-date security patches in cloud-native environments and demonstrates how seemingly edge-case security flaws can have significant operational consequences. Organizations should also consider implementing additional authentication layers and monitoring mechanisms to provide defense-in-depth against similar vulnerabilities that might exist in their service mesh architectures.