Eclipse Californium is a Java implementation of RFC7252 - Constrained Application Protocol for IoT Cloud services. In versions prior to 3.7.0, and 2.7.4, Californium is vulnerable to a Denial of Service. Failing handshakes don't cleanup counters for throttling, causing the threshold to be reached without being released again. This results in permanently dropping records. The issue was reported for certificate based handshakes, but may also affect PSK based handshakes. It generally affects client and server as well. This issue is patched in version 3.7.0 and 2.7.4. There are no known workarounds. main: commit 726bac57659410da463dcf404b3e79a7312ac0b9 2.7.x: commit 5648a0c27c2c2667c98419254557a14bac2b1f3f

In Eclipse Californium version 2.0.0 to 2.7.2 and 3.0.0-3.5.0 a DTLS resumption handshake falls back to a DTLS full handshake on a parameter mismatch without using a HelloVerifyRequest. Especially, if used with certificate based cipher suites, that results in message amplification (DDoS other peers) and high CPU load (DoS own peer). The misbehavior occurs only with DTLS_VERIFY_PEERS_ON_RESUMPTION_THRESHOLD values larger than 0.

In Eclipse Californium version 2.0.0 to 2.6.4 and 3.0.0-M1 to 3.0.0-M3, the certificate based (x509 and RPK) DTLS handshakes accidentally succeeds without verifying the server side's signature on the client side, if that signature is not included in the server's ServerKeyExchange.

In Eclipse Californium version 2.3.0 to 2.6.0, the certificate based (x509 and RPK) DTLS handshakes accidentally fails, because the DTLS server side sticks to a wrong internal state. That wrong internal state is set by a previous certificate based DTLS handshake failure with TLS parameter mismatch. The DTLS server side must be restarted to recover this. This allow clients to force a DoS.