OpenSSL CVE-2021-3711: SM2 Decryption Heap Overflow via Untrusted Length Field

CVE-2021-3711 is a heap buffer overflow vulnerability in OpenSSL 1.1.1k (and earlier) affecting the SM2 elliptic curve cryptography decryption function. The vulnerability allows an attacker to craft a malicious SM2 ciphertext that causes the decryption function to write past the bounds of the plaintext output buffer. This can lead to memory corruption and potential code execution.