CVE-2011-1499 in Tinyproxy
Summary
by MITRE
acl.c in Tinyproxy before 1.8.3, when an Allow configuration setting specifies a CIDR block, permits TCP connections from all IP addresses, which makes it easier for remote attackers to hide the origin of web traffic by leveraging the open HTTP proxy server.
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Analysis
by VulDB Data Team • 11/05/2021
The vulnerability identified as CVE-2011-1499 affects Tinyproxy versions prior to 1.8.3 and represents a critical misconfiguration flaw in the access control implementation. This issue stems from how Tinyproxy processes the Allow configuration directive when CIDR block specifications are used, creating a significant security gap that undermines the intended proxy filtering mechanisms. The flaw allows malicious actors to bypass IP address restrictions and establish connections from any IP address within the network, effectively neutralizing the access control measures that should limit proxy usage to authorized networks.
The technical implementation of this vulnerability resides in the acl.c file where the CIDR block parsing logic fails to properly enforce access restrictions. When administrators configure Tinyproxy with Allow directives specifying CIDR notation such as 192.168.1.0/24, the software incorrectly processes these specifications and permits connections from any IP address rather than restricting access to the specified network range. This misimplementation creates an open proxy condition where the HTTP proxy server becomes a conduit for anonymous web traffic without proper access controls. The flaw essentially transforms the intended network access control into a permissive connection mechanism that can be exploited by remote attackers.
The operational impact of this vulnerability extends beyond simple access control bypass and creates significant risks for organizations relying on Tinyproxy for network security. Attackers can leverage this vulnerability to establish anonymous web browsing sessions through the proxy server, making it difficult for network administrators to trace the origin of web traffic or implement proper monitoring. This capability enables malicious actors to hide their true IP addresses while conducting web activities, potentially facilitating data exfiltration, malicious web scraping, or other unauthorized network activities. The vulnerability directly enables man-in-the-middle attacks and traffic interception scenarios that would otherwise be prevented by proper access controls, creating an environment where network traffic can be monitored and manipulated without detection.
This vulnerability aligns with CWE-284, which addresses improper access control issues, and represents a classic example of how misconfigured access control mechanisms can create security holes in network services. From an ATT&CK framework perspective, this vulnerability maps to TA0011 (Command and Control) and TA0006 (Credential Access) where attackers can establish persistent connections through the open proxy and potentially harvest credentials or sensitive information from web sessions. The flaw also contributes to TA0005 (Defense Evasion] by allowing attackers to mask their network activities and bypass network monitoring systems that depend on proper access control enforcement.
Organizations should immediately upgrade to Tinyproxy version 1.8.3 or later where this vulnerability has been addressed through proper CIDR block validation and enforcement. Network administrators should implement additional monitoring measures to detect unauthorized proxy usage patterns and consider deploying network segmentation strategies that limit direct access to proxy servers. The mitigation strategy should include comprehensive testing of access control configurations to ensure that CIDR blocks are properly enforced and that no unauthorized IP addresses can establish connections through the proxy service. Regular security audits of proxy configurations should be conducted to prevent similar misconfigurations that could create analogous security vulnerabilities in the network infrastructure.