Mbed TLS 3.x vulnerability: Incorrect handling of certificate usage

CVE-2024-45159

Summary

An issue in Mbed TLS versions prior to 3.6.1 affects TLS 1.3 when a server allows optional client authentication. If a client provides a certificate lacking appropriate keyUsage or extKeyUsage extension values, the function mbedtls_ssl_get_verify_result() fails to set the MBEDTLS_X509_BADCERT_KEY_USAGE bits. This oversight allows an attacker to exploit certificates not intended for TLS client authentication, enabling potential security risks. The vulnerability is limited to servers utilizing optional client authentication; strict configurations requiring client credentials will trigger a handshake failure, thwarting such attacks.

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