CVE-2025-27371 in Connect
Summary
by MITRE • 03/03/2025
In certain IETF OAuth 2.0-related specifications, when the JSON Web Token Profile for OAuth 2.0 Client Authentication mechanism is used, there are ambiguities in the audience values of JWTs sent to authorization servers. The affected RFCs may include RFC 7523, and also RFC 7521, RFC 7522, RFC 9101 (JAR), and RFC 9126 (PAR).
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 06/01/2025
The vulnerability identified as CVE-2025-27371 stems from ambiguities in the audience value handling within JSON Web Token profiles for OAuth 2.0 client authentication mechanisms. This weakness affects implementations that rely on the IETF specifications for secure token exchange between clients and authorization servers. The affected standards include RFC 7523 which defines the JWT profile for OAuth 2.0 client authentication, alongside RFC 7521 for JWT authorization grants, RFC 7522 for JWT bearer tokens, RFC 9101 for JWT Authorization Request, and RFC 9126 for Pushed Authorization Requests. These specifications collectively establish the framework for secure client authentication using JWTs in OAuth 2.0 environments.
The technical flaw manifests when JWTs containing client authentication information are sent to authorization servers, where the audience value may be interpreted inconsistently across different implementations. This ambiguity creates potential security risks as authorization servers might accept tokens intended for different audiences or reject valid tokens due to misinterpretation of audience claims. The vulnerability is classified under CWE-284 Access Control Issues, specifically related to improper access control in token validation mechanisms. The ambiguity in audience handling can lead to privilege escalation scenarios where unauthorized clients might gain access to resources they should not be permitted to access.
The operational impact of this vulnerability extends beyond simple authentication failures to potentially enable sophisticated attacks against OAuth 2.0 implementations. Attackers could exploit the ambiguous audience handling to perform token substitution attacks, where valid JWTs intended for one authorization server might be redirected to another server with different audience requirements. This creates a pathway for unauthorized access to protected resources and could lead to data breaches or privilege escalation within systems relying on these specifications. The vulnerability affects a broad range of implementations including those using the JWT profile for client authentication, authorization grants, and bearer tokens, making it particularly concerning for organizations with extensive OAuth 2.0 deployments.
Mitigation strategies for CVE-2025-27371 should focus on implementing strict audience validation mechanisms within authorization servers and ensuring consistent interpretation of audience claims across all JWT implementations. Organizations should update their OAuth 2.0 implementations to explicitly validate audience values against known acceptable audiences and implement proper token introspection capabilities to verify token integrity. The mitigation approach aligns with ATT&CK technique T1566.001 for credential access through social engineering and T1078.004 for valid accounts through compromised credentials, as the vulnerability could enable attackers to leverage valid tokens inappropriately. Additionally, implementing comprehensive logging and monitoring of authentication attempts can help detect potential exploitation attempts, while regular security assessments of OAuth 2.0 implementations should be conducted to identify and address similar ambiguities in other RFC specifications.