The HTTPD binary in multiple ZTE routers has a stack-based buffer overflow vulnerability in rsa_decrypt function. This function is an API wrapper for LUA to decrypt RSA encrypted ciphertext, the decrypted data is stored on the stack without checking its length. An authenticated attacker can get RCE as root by exploiting this vulnerability.
https://wr3nchsr.github.io/zte-multiple-routers-httpd-vulnerabilities-advisory/