CVE-2007-0838 in FreeProxy
Summary
by MITRE
FreeProxy before 3.92 Build 1626 allows malicious users to cause a denial of service (infinite loop) via a HOST: header with a hostname and port number that refers to the server itself.
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Analysis
by VulDB Data Team • 07/13/2021
The vulnerability identified as CVE-2007-0838 affects FreeProxy versions prior to 3.92 Build 1626, representing a significant security flaw that can be exploited to cause denial of service conditions. This issue stems from improper handling of HTTP HOST headers within the proxy server implementation, creating a potential attack vector that malicious users can leverage to disrupt service availability. The vulnerability specifically manifests when a HOST header contains a hostname and port number that references the server itself, leading to a condition where the proxy enters an infinite loop during request processing.
The technical flaw resides in the proxy server's request parsing and validation mechanisms, where it fails to properly sanitize or validate HOST header values that reference the same server. When such malformed headers are processed, the FreeProxy software enters a recursive or circular reference scenario that causes it to continuously loop in its processing logic. This infinite loop consumes system resources and effectively renders the proxy service unavailable to legitimate users, constituting a classic denial of service attack pattern. The vulnerability demonstrates poor input validation and lacks proper boundary checks that would normally prevent such recursive processing scenarios.
From an operational impact perspective, this vulnerability creates a critical risk for organizations relying on FreeProxy for network traffic management and filtering. The infinite loop condition can cause complete service disruption, potentially affecting multiple users and applications that depend on the proxy server for internet connectivity. Network administrators may experience prolonged service outages while investigating and resolving the issue, leading to productivity losses and potential business disruption. The vulnerability is particularly concerning because it requires minimal effort to exploit, making it an attractive target for attackers seeking to disrupt services without sophisticated attack techniques.
The flaw aligns with CWE-400, which addresses improper handling of input that can lead to resource exhaustion, and relates to ATT&CK technique T1499.004 for network denial of service attacks. Organizations should implement immediate mitigations including updating to FreeProxy version 3.92 Build 1626 or later, which contains the necessary patches to properly validate HOST headers. Additional protective measures include implementing proxy server rate limiting, configuring input validation rules for HOST headers, and establishing monitoring systems to detect unusual processing patterns that might indicate exploitation attempts. Network segmentation and firewall rules can also help limit the impact of such attacks by restricting access to the vulnerable proxy server from untrusted networks.