CVE-2013-4123 in Squid
Summary
by MITRE
client_side_request.cc in Squid 3.2.x before 3.2.13 and 3.3.x before 3.3.8 allows remote attackers to cause a denial of service via a crafted port number in a HTTP Host header.
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Analysis
by VulDB Data Team • 11/27/2024
The vulnerability identified as CVE-2013-4123 represents a critical denial of service flaw within the Squid proxy server software, specifically affecting versions 3.2.x prior to 3.2.13 and 3.3.x prior to 3.3.8. This issue resides in the client_side_request.cc component of the Squid codebase, which handles client-side request processing. The flaw manifests when the proxy server processes HTTP Host headers containing malformed port numbers, creating a condition where the software fails to properly validate input parameters before attempting to establish connections. This vulnerability falls under the CWE-129 weakness category, which encompasses issues related to improper validation of input boundaries, and aligns with ATT&CK technique T1499.004 for network denial of service attacks. The vulnerability enables remote attackers to exploit the proxy server's handling of malformed HTTP Host headers, potentially causing the service to crash or become unresponsive.
The technical exploitation of this vulnerability occurs when an attacker crafts a HTTP Host header containing an invalid or excessively large port number that exceeds the expected range. When Squid processes this malformed header, the software attempts to parse and validate the port value without proper bounds checking, leading to integer overflow conditions or memory corruption scenarios. The proxy server's request processing pipeline fails to properly sanitize the port number extracted from the Host header, allowing the malformed input to propagate through the system's connection handling mechanisms. This flaw specifically impacts the connection establishment phase where Squid attempts to create outbound connections based on the parsed port information, causing the software to enter an unstable state that results in service interruption.
The operational impact of CVE-2013-4123 extends beyond simple service disruption, as it can affect organizations relying on Squid as a critical network infrastructure component. When exploited, this vulnerability can cause complete denial of service for proxy services, potentially disrupting thousands of concurrent users who depend on the proxy server for internet access, content filtering, or caching operations. The vulnerability is particularly concerning in enterprise environments where Squid serves as a primary web proxy, as it can be exploited without requiring authentication or advanced privileges. Organizations may experience cascading effects when the proxy service becomes unavailable, impacting downstream applications, network performance, and user productivity. The attack vector is easily accessible over the network, making it a preferred target for automated scanning and exploitation tools that seek to identify vulnerable systems.
Mitigation strategies for CVE-2013-4123 should focus on immediate patching of affected Squid versions to the recommended secure releases, specifically upgrading to Squid 3.2.13 or 3.3.8 and later. Network administrators should implement additional defensive measures including firewall rules that restrict access to proxy ports from untrusted networks, and deployment of intrusion detection systems that can identify suspicious Host header patterns. Configuration hardening should include implementing strict input validation for HTTP headers, enabling logging of suspicious requests, and monitoring proxy server behavior for unusual connection patterns. Organizations should also consider implementing rate limiting mechanisms to prevent rapid exploitation attempts and establish automated monitoring procedures to detect service disruptions. The vulnerability demonstrates the importance of proper input validation in network services and highlights the need for comprehensive security testing of proxy server implementations to prevent similar issues in the future.