CVE-2018-9192 in FortiOS
Summary
by MITRE
A plaintext recovery of encrypted messages or a Man-in-the-middle (MiTM) attack on RSA PKCS #1 v1.5 encryption may be possible without knowledge of the server's private key. Fortinet FortiOS 5.4.6 to 5.4.9, 6.0.0 and 6.0.1 are vulnerable by such attack under SSL Deep Inspection feature when CPx being used.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 01/21/2025
The vulnerability identified as CVE-2018-9192 represents a critical weakness in the cryptographic implementation of Fortinet FortiOS appliances that enables attackers to perform plaintext recovery or man-in-the-middle attacks against RSA PKCS #1 v1.5 encrypted communications. This flaw specifically affects versions 5.4.6 through 5.4.9 and 6.0.0 through 6.0.1 when the SSL Deep Inspection feature is active and CPx (Crypto Processing eXtension) is being utilized. The vulnerability stems from improper implementation of the RSA encryption protocol that allows adversaries to exploit weaknesses in the padding scheme used for message encryption.
The technical flaw manifests through the improper handling of RSA PKCS #1 v1.5 encryption padding during SSL inspection processes. When SSL Deep Inspection is enabled, the FortiOS appliance intercepts and examines encrypted traffic to identify potential threats or content violations. The vulnerability occurs because the system fails to properly validate the padding structure of RSA encrypted messages, allowing attackers to manipulate the encrypted data without possessing the server's private key. This weakness falls under CWE-327, which specifically addresses the use of insecure cryptographic algorithms and improper implementation of cryptographic protocols.
The operational impact of this vulnerability extends beyond simple data interception, as it enables sophisticated attack vectors that can compromise the confidentiality and integrity of encrypted communications. Attackers can exploit this weakness to recover plaintext messages from encrypted traffic, effectively bypassing the security assurances that RSA encryption is designed to provide. The vulnerability is particularly concerning in enterprise environments where SSL Deep Inspection is commonly deployed for security monitoring and threat detection. Organizations using FortiOS appliances with this feature enabled face significant risk of data breaches, as the attack can be executed without requiring access to the private key, making it especially dangerous for applications that rely on RSA encryption for secure communication.
Mitigation strategies for CVE-2018-9192 require immediate action from affected organizations, including the deployment of Fortinet's security patches and firmware updates that address the specific cryptographic implementation flaw. System administrators should disable SSL Deep Inspection functionality when it is not strictly required for security operations, as this feature is the primary vector for exploitation. The implementation of alternative encryption methods that do not rely on vulnerable PKCS #1 v1.5 padding schemes should be considered, along with enhanced monitoring for suspicious network activity that might indicate exploitation attempts. Organizations should also review their overall security architecture to ensure that the use of SSL inspection is properly justified and that appropriate compensating controls are implemented to maintain security posture while continuing to meet compliance requirements. The vulnerability aligns with ATT&CK technique T1566, which covers phishing with malicious attachments and links, as attackers can leverage this weakness to gain access to sensitive information through compromised encrypted communications.