CVE-2026-93304 (D)TLS 1.2 client accepts early ChangeCipherSpec before ClientKeyExchange
An attacker can inject early ChangeCipherSpec messages to bypass TLS handshake validation, allowing them to send data accepted as authentic by the client.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-93304?
CVE-2026-93304 is a medium-severity vulnerability in Wolfssl Wolfssl, published on 27 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A (D)TLS 1.2 client can accept a ChangeCipherSpec message before it has sent its ClientKeyExchange. No master secret has been derived at that point, so the client installs read keys derived from a known (deterministic) key and checks the server's Finished against that same key. An out-of-order ChangeCipherSpec can therefore be used by an attacker to complete the handshake in place of the server and send data the client accepts as authentic. The client's own traffic still uses correctly derived keys, so the attacker cannot read it, and the genuine server never completes the handshake. DTLS 1.2 clients are exposed because a datagram read can deliver the out-of-order records on its own. TLS 1.2 clients are exposed when the application supplies received bytes with wolfSSL_inject() or enables read ahead. For certificate suites, the attacker must be in a man-in-the-middle position. For PSK (Pre Shared Key) connections, any fake server can succeed without knowing the PSK.
Weakness: CWE-696
Which versions are affected by CVE-2026-93304?
It affects 1 product.
Products include Wolfssl Wolfssl.
How do I fix CVE-2026-93304?
No fix has been published for CVE-2026-93304 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-93304 being exploited?
There is no known exploitation of CVE-2026-93304 in the wild and no public exploit code.
Other vulnerabilities in Wolfssl Wolfssl
Sources
Also known as AZL-105194, DEBIAN-CVE-2026-93304, GHSA-vpg5-xh2g-4x3c, UBUNTU-CVE-2026-93304.