An issue was discovered in Mbed TLS before 2.28.1 and 3.x before 3.2.0. In some configurations, an unauthenticated attacker can send an invalid ClientHello message to a DTLS server that causes a heap-based buffer over-read of up to 255 bytes. This can cause a server crash or possibly information disclosure based on error responses. Affected configurations have MBEDTLS SSL DTLS CLIENT PORT REUSE enabled and MBEDTLS SSL IN CONTENT LEN less than a threshold that depends on the configuration: 258 bytes if using mbedtls ssl cookie check, and possibly up to 571 bytes with a custom cookie check function.