Fortinet FortiOS Hard-coded Cryptographic Key in Configuration Backup Vulnerability (CVE-2019-6693) Advisory

1. Vulnerability Overview & Root Cause

This vulnerability (CVE-2019-6693) arises from the use of a hard-coded cryptographic key within Fortinet FortiOS to encrypt sensitive data inside configuration backup files. When administrators generate a backup without explicitly defining a custom password, FortiOS defaults to using a static, built-in cryptographic key to obfuscate sensitive parameters. This design flaw allows anyone who obtains the backup file and possesses knowledge of the hard-coded key to reverse the encryption.

2. Exploitation Mechanics & Attack Scenario

The exploitation begins when an attacker gains read access to a FortiOS configuration backup file (.conf). This can be achieved through compromised low-privilege administrator accounts, insecure backup storage servers, or accidental exposure of configuration files. Using publicly known decryption scripts or tools containing the extracted hard-coded key, the attacker decrypts the backup file. This exposes sensitive credentials, such as user passwords (excluding the super-administrator password), SSL/TLS private key passphrases, and High Availability (HA) cluster pre-shared keys, enabling lateral movement and full network compromise.

3. Infrastructure & Business Impact

As a vulnerability listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, CVE-2019-6693 poses a severe and active threat to enterprise networks. Exposure of SSL private keys allows attackers to perform man-in-the-middle (MitM) attacks or decrypt intercepted network traffic. Furthermore, compromised user credentials can facilitate unauthorized VPN access, bypassing perimeter defenses and leading to potential ransomware deployment or data exfiltration.