CVE-2026-93304 describes a vulnerability in (D)TLS 1.2 clients where the client accepts a ChangeCipherSpec message before sending its ClientKeyExchange. Since no master secret is derived at that point, the client uses read keys from a known deterministic key to verify the server's Finished message. An attacker can exploit this out-of-order ChangeCipherSpec to impersonate the server and send data the client accepts as authentic. This affects DTLS 1.2 clients due to datagram delivery of out-of-order records, and TLS 1.2 clients when wolfSSL_inject() is used or read ahead is enabled. For certificate-based suites, a man-in-the-middle is required; for PSK connections, any fake server can succeed without knowing the PSK. The client's own transmitted data remains secure, and the real server does not complete the handshake.

The vulnerability allows an attacker to impersonate the server and send data that the client accepts as authentic, compromising data integrity on the client side. However, the attacker cannot decrypt or read the client's outgoing traffic, and the genuine server never completes the handshake. For certificate-based suites, exploitation requires a man-in-the-middle position. For PSK connections, any fake server can exploit the flaw without the PSK. The CVSS score of 3.7 reflects a medium impact primarily on data integrity.

No patch or official fix information is provided. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Mitigation should focus on avoiding use of wolfSSL_inject() or read ahead features in TLS 1.2 clients and ensuring proper handling of ChangeCipherSpec messages. Network defenses to prevent man-in-the-middle attacks are also relevant for certificate-based suites.