CVE-2021-26095 in FortiMail
Summary
by MITRE • 07/20/2021
The combination of various cryptographic issues in the session management of FortiMail 6.4.0 through 6.4.4 and 6.2.0 through 6.2.6, including the encryption construction of the session cookie, may allow a remote attacker already in possession of a cookie to possibly reveal and alter or forge its content, thereby escalating privileges.
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Analysis
by VulDB Data Team • 07/26/2021
The vulnerability identified as CVE-2021-26095 represents a critical weakness in the session management implementation of FortiMail email security appliances, affecting versions 6.4.0 through 6.4.4 and 6.2.0 through 6.2.6. This cryptographic flaw specifically targets the session cookie encryption mechanism, creating a pathway for remote attackers to exploit existing session tokens and manipulate their contents. The vulnerability stems from improper implementation of cryptographic constructs used to secure session identifiers, which undermines the fundamental security assumptions of the application's authentication system.
The technical flaw manifests through multiple cryptographic weaknesses that collectively weaken the session cookie protection mechanism. Attackers who have already obtained a valid session cookie can leverage these vulnerabilities to decrypt, modify, or forge session tokens, effectively bypassing authentication controls. This issue falls under the category of weak cryptographic implementation as defined by CWE-327, specifically addressing the use of insecure cryptographic algorithms or improper implementation of cryptographic functions. The vulnerability enables privilege escalation by allowing attackers to assume the identity of legitimate users and access administrative functions that should be restricted to authorized personnel only.
The operational impact of this vulnerability extends beyond simple session hijacking, as it provides attackers with the capability to perform unauthorized administrative actions within the FortiMail environment. Once an attacker successfully exploits this vulnerability, they can gain elevated privileges and potentially access sensitive email data, modify system configurations, or establish persistent access to the email security infrastructure. This represents a significant threat to email security and compliance, particularly in enterprise environments where FortiMail appliances protect critical communication channels and sensitive data repositories. The vulnerability directly impacts the integrity and confidentiality of email communications by undermining the authentication and authorization mechanisms that should protect these systems.
Organizations affected by this vulnerability should immediately implement mitigations including updating to patched versions of FortiMail software, implementing additional session management controls, and monitoring for suspicious authentication patterns. The remediation process should involve comprehensive security assessments of the email infrastructure and review of session management policies. Security teams should also consider implementing network segmentation, enhanced logging and monitoring of authentication events, and regular security audits to detect potential exploitation attempts. This vulnerability aligns with several ATT&CK techniques including credential access and privilege escalation, making it particularly concerning for organizations that rely on FortiMail for email security operations and require robust protection against sophisticated adversaries.