CVE-2005-3058 in FortiOS
Summary
by MITRE
Interpretation conflict in Fortinet FortiGate 2.8, running FortiOS 2.8MR10 and v3beta, allows remote attackers to bypass the URL blocker via an (1) HTTP request terminated with a line feed (LF) and not carriage return line feed (CRLF) or (2) HTTP request with no Host field, which is still processed by most web servers without violating RFC2616.
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Analysis
by VulDB Data Team • 12/07/2024
The vulnerability described in CVE-2005-3058 represents a critical interpretation conflict within Fortinet FortiGate 2.8 devices running specific FortiOS versions including 2.8MR10 and v3beta. This flaw exploits the inconsistent handling of HTTP protocol elements by the device's URL filtering mechanisms, creating a significant security gap that adversaries can leverage to circumvent content filtering controls. The vulnerability specifically targets the device's ability to properly parse and validate HTTP requests, demonstrating how protocol interpretation differences can lead to security bypasses in network security appliances.
The technical implementation of this vulnerability stems from the FortiGate device's inconsistent handling of HTTP request termination sequences and header validation. Attackers can exploit this by sending HTTP requests terminated with only a line feed character (LF) instead of the standard carriage return line feed (CRLF) combination required by RFC2616. Additionally, the vulnerability allows bypassing through HTTP requests that lack the mandatory Host field, a scenario that web servers typically process without issue while still violating the HTTP specification. This dual exploitation method demonstrates a fundamental flaw in the device's HTTP request parsing logic where it fails to properly validate the protocol compliance of incoming requests before applying content filtering rules.
The operational impact of this vulnerability extends beyond simple bypass of URL filtering, potentially allowing attackers to access restricted content, exfiltrate data, or establish command and control communications through filtered network paths. Network administrators who rely on FortiGate's URL filtering capabilities for security policy enforcement face significant risk as this vulnerability can be exploited remotely without authentication, making it particularly dangerous in enterprise environments where content filtering is critical for maintaining security posture. The vulnerability essentially undermines the device's core security function by allowing malicious traffic to slip through content filtering mechanisms that should have blocked it based on URL content or destination.
This vulnerability aligns with CWE-20, "Improper Input Validation," and demonstrates how improper handling of input protocols can lead to security bypasses in network appliances. From an ATT&CK framework perspective, this vulnerability maps to T1071.004, "Application Layer Protocol: DNS," and T1566, "Phishing," as it enables bypass of security controls that would otherwise prevent access to malicious domains or phishing sites. The vulnerability also relates to T1059, "Command and Scripting Interpreter," as it could potentially allow attackers to bypass URL filtering that would normally prevent access to command and control infrastructure. Organizations should consider this vulnerability as part of a broader attack chain that could lead to more sophisticated compromises when combined with other network-level attacks.
Mitigation strategies for this vulnerability should include immediate firmware updates to patched versions of FortiOS that properly handle HTTP request termination sequences and header validation. Network administrators should also implement additional monitoring for HTTP requests with non-standard termination sequences and missing Host fields, as these patterns may indicate exploitation attempts. The device configuration should be reviewed to ensure proper HTTP protocol compliance checking is enabled, and network segmentation should be implemented to limit the impact of potential exploitation. Additionally, organizations should consider implementing supplementary security controls such as deep packet inspection or web application firewalls to provide additional layers of protection against similar protocol-based attacks that exploit interpretation conflicts in network security appliances.