CVE-2018-9194 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 VIP SSL feature when CPx being used.
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Analysis
by VulDB Data Team • 01/21/2025
The vulnerability described in CVE-2018-9194 represents a critical weakness in the cryptographic implementation of Fortinet FortiOS SSL VPN services, specifically affecting versions 5.4.6 through 5.4.9 and 6.0.0 through 6.0.1. This flaw exists within the VIP SSL feature when utilizing CPx (Crypto Processing eXtension) functionality, creating a pathway for attackers to potentially recover plaintext messages that were originally encrypted using RSA PKCS #1 v1.5 padding. The vulnerability stems from improper implementation of the RSA encryption scheme that allows for exploitation without requiring access to the server's private key, fundamentally undermining the security assurances provided by the SSL/TLS protocol stack. Such weaknesses in cryptographic implementations are particularly dangerous as they can enable adversaries to intercept and decrypt sensitive communications passing through the affected FortiOS appliances.
The technical nature of this vulnerability lies in the improper handling of RSA PKCS #1 v1.5 encryption padding, which creates mathematical weaknesses that can be exploited through specific attack vectors. The flaw specifically affects the SSL VPN functionality when the CPx hardware acceleration module is enabled, suggesting that the vulnerability is not merely a software implementation issue but potentially involves hardware-software interactions that compound the risk. When the VIP SSL feature processes encrypted communications, the flawed padding mechanism allows for potential plaintext recovery or man-in-the-middle attacks, where an attacker can manipulate the cryptographic handshake process to obtain cleartext data. This vulnerability aligns with CWE-327, which addresses the use of weak encryption algorithms and improper implementation of cryptographic primitives, and more specifically with CWE-328, which covers the use of weak hashing algorithms in cryptographic functions.
The operational impact of CVE-2018-9194 extends far beyond simple data confidentiality breaches, as it enables attackers to potentially gain unauthorized access to sensitive corporate communications, user credentials, and business-critical information transmitted through the affected SSL VPN infrastructure. Organizations relying on Fortinet FortiOS appliances for remote access and secure communications face significant risk of data exfiltration, credential theft, and potential lateral movement within their networks if attackers successfully exploit this vulnerability. The attack vector requires minimal privileges and does not necessitate knowledge of the server's private key, making it particularly dangerous for organizations that may not have comprehensive monitoring of their SSL VPN traffic or that rely solely on the appliance's built-in security mechanisms. This vulnerability can be leveraged as an initial access point for more sophisticated attacks, potentially enabling privilege escalation and persistent threats within the network environment.
Mitigation strategies for CVE-2018-9194 require immediate attention from security administrators, beginning with the immediate upgrade of affected Fortinet FortiOS appliances to patched versions that address the RSA padding implementation weakness. Organizations should also consider implementing additional monitoring and detection measures to identify potential exploitation attempts, including network traffic analysis for anomalous SSL handshake patterns and cryptographic operations. The implementation of alternative encryption methods such as RSA-OAEP padding or transitioning to more secure cryptographic protocols can provide additional defense in depth. Security teams should also conduct comprehensive vulnerability assessments of their SSL VPN infrastructure and review access controls to minimize potential impact if exploitation occurs. This vulnerability demonstrates the critical importance of proper cryptographic implementation and the need for continuous security validation of network infrastructure components, particularly those handling sensitive data communications. The remediation process should also include thorough testing of patched configurations to ensure that the upgrade does not introduce compatibility issues with existing network services while maintaining the integrity of the cryptographic security posture.