CVE-2023-33307 in FortiOS
Summary
by MITRE • 06/16/2023
A null pointer dereference in Fortinet FortiOS before 7.2.5 and before 7.0.11, FortiProxy before 7.2.3 and before 7.0.9 allows attacker to denial of sslvpn service via specifically crafted request in network parameter.
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Analysis
by VulDB Data Team • 07/14/2023
The vulnerability identified as CVE-2023-33307 represents a critical null pointer dereference flaw affecting Fortinet FortiOS and FortiProxy products across multiple version ranges. This security weakness exists within the SSLVPN service implementation and can be exploited through specifically crafted network parameter requests that trigger the vulnerable code path. The vulnerability stems from insufficient input validation and error handling mechanisms within the SSLVPN subsystem, where the application fails to properly validate user-supplied parameters before attempting to dereference pointers that may remain uninitialized or set to null values. The flaw manifests when processing network parameters submitted through SSLVPN connections, creating an opportunity for remote attackers to disrupt service availability without requiring authentication credentials.
The technical execution of this vulnerability follows a well-defined attack pattern that aligns with CWE-476, which specifically addresses null pointer dereference conditions in software implementations. When an attacker crafts a malicious request containing malformed network parameters, the FortiOS or FortiProxy system attempts to process these inputs through its SSLVPN service handler. During this processing, the application fails to validate whether certain pointer variables have been properly initialized, leading to a scenario where a null pointer is dereferenced during the service operation. This condition results in an application crash or termination, effectively causing a denial of service condition that prevents legitimate users from accessing SSLVPN services. The vulnerability operates at the application layer and can be initiated through network-based attacks that target the SSLVPN service endpoints.
The operational impact of CVE-2023-33307 extends beyond simple service disruption, as it represents a significant threat to business continuity and network availability for organizations relying on Fortinet SSLVPN solutions. The vulnerability can be exploited remotely without authentication, making it particularly dangerous for environments where SSLVPN services serve as primary access points for remote workers or branch office connections. Organizations may experience extended periods of service unavailability that can impact productivity, access to critical systems, and overall network infrastructure reliability. The attack vector is particularly concerning because it can be executed through standard network traffic without requiring specialized tools or privileged access, making it accessible to a broad range of threat actors from casual attackers to organized cybercriminal groups. This vulnerability directly maps to ATT&CK technique T1499.004, which covers network denial of service attacks targeting service availability.
Mitigation strategies for CVE-2023-33307 should prioritize immediate patching of affected Fortinet FortiOS and FortiProxy systems to versions 7.2.5 and 7.0.11 for FortiOS, and 7.2.3 and 7.0.9 for FortiProxy, as these releases contain the necessary code fixes to prevent the null pointer dereference condition. Network administrators should also implement temporary network-level mitigations such as access control lists that restrict access to SSLVPN service endpoints until patches can be deployed, though this approach provides only partial protection. Additionally, organizations should enhance their monitoring capabilities to detect unusual patterns in SSLVPN service requests that may indicate exploitation attempts, as well as implement intrusion detection systems that can identify and block malicious network parameter sequences. The vulnerability highlights the importance of robust input validation and error handling practices in network security appliances, emphasizing the need for comprehensive security testing and code review processes to prevent similar issues in future releases. Organizations should also consider implementing redundant SSLVPN services or alternative access methods to maintain business continuity during patching operations and to provide failover capabilities in case of exploitation attempts.