CVE-2023-34758

Vulnerability

Analysis

CVE-2023-34758 is an improper cryptographic implementation in the Sliver command-and-control framework, affecting versions 1.5.x through 1.5.39. The vulnerability stems from a flawed implementation of the ECDH key exchange scheme used by Sliver implants and servers, which fails to achieve the claimed forward secrecy. According to the Sliver documentation, the framework was designed to provide partial forward secrecy by encrypting session keys with the server's public key; however, the actual implementation allowed an attacker with access to the implant binary to recover session keys without needing the server's private key [1][2].

Exploitation

An attacker in a man-in-the-middle (MitM) position—such as on the same network segment or via compromised infrastructure—can exploit this vulnerability by intercepting network traffic between a Sliver implant and its C2 server. With access to the implant executable (which contains hard-coded cryptographic material), the attacker can decrypt the ECDH key exchange, recover the session key, and then forge or modify responses. The official advisory notes that the MitM does not require the server's private key, only the implant binary, making the attack practical in many operational scenarios [1][2].

Impact

Successful exploitation grants the attacker full decryption of all transmitted data between the implant and server, including command and control messages. Moreover, the MitM can actively compromise the connection to execute arbitrary commands supported by the implant on the compromised device, effectively taking control of the implant. This can lead to complete loss of confidentiality, integrity, and availability of the C2 channel, allowing the attacker to issue arbitrary commands, exfiltrate data, or pivot to other systems [1].

Mitigation

The vulnerability was remedied by the Sliver development team in a subsequent commit that replaced the vulnerable ECDH-based crypto implementation with a more robust scheme using the filippo.io/age library and X25519 key exchange [3][4]. Users are strongly advised to update their Sliver server and implant artifacts to a patched version (post-1.5.39) to prevent MitM attacks. There is no evidence that this CVE has been added to the CISA Known Exploited Vulnerabilities (KEV) catalog as of this writing, but given the criticality, immediate patching is recommended.