DrayTek Vigor3900 1.5.1.3 allows attackers to inject malicious commands into mainfunction.cgi and execute arbitrary commands by calling the sign_cacertificate function.
https://github.com/fu37kola/cve/blob/main/DrayTek/Vigor3900/1.5.1.3/DrayTek_Vigor_3900_1.5.1.3.pdf