aria2c Improper Certificate Validation Vulnerability Allowing Misuse of Compromised Certificates for TLS Server Authentication

A vulnerability exists in aria2c versions through 1.37.0, where the application improperly validates server certificates with incorrect Extended Key Usage (EKU). This flaw allows attackers to exploit compromised certificates, originally issued for different purposes, by reusing them for TLS server authentication. The vulnerability arises because aria2c fails to enforce correct EKU requirements, potentially enabling man-in-the-middle attacks or unauthorized access to resources.

Impact

Exploitation of this vulnerability could lead to improper authentication of TLS servers, allowing attackers to intercept or manipulate communications.

Reproduction

The vulnerability can be reproduced by generating a private key and an X.509 certificate with an incorrect EKU, such as one intended for client authentication instead of server authentication. After creating a simple TLS server using the invalid certificate, aria2c can be used to connect to the server. Despite the certificate being invalid for server authentication, aria2c will accept the connection, demonstrating the improper validation.