jasperla / realtek_turnkey_decrypter

CVE-2019-15802 decrypter

The Zyxel firmware for the GS1900 switches, at least version 2.40(AAHH.2)C0, contains a hardcoded parameters which are used for AES256-CBC encryption an decryption of passwords. These parameters (IV, salt and password) are fixed for all devices running the firmware.

salt[] = "1A3BB2F78D6EC7D8";
iv[32] = "2268BA68768B58C3687D4F205923A741";
key_data[64] = "EC14D4F5BC6B9A3766D31EF9A1BB854121FB938B606462C70B2D0E26549C486A";

A longer write-up of this (and the associated issues) is available here and Zyxel's advisory is here.

decrypter

Based on the code in libsal.so (responsible the encryption and decryption in the firmware) I hacked up a quick tool to demonstrate how these hardcoded parameters can be used to decrypt passwords, e.g. in combination with CVE-2019-15799.

The hardcoded credentials in the firmware (CVE-2019-15801) were also encrypted with this key.