CVE-2010-0639 in Squid
Summary
by MITRE
The htcpHandleTstRequest function in htcp.c in Squid 2.x before 2.6.STABLE24 and 2.7 before 2.7.STABLE8, and htcp.cc in 3.0 before 3.0.STABLE24, allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via crafted packets to the HTCP port.
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Analysis
by VulDB Data Team • 04/30/2026
The vulnerability identified as CVE-2010-0639 represents a critical denial of service flaw affecting Squid proxy servers across multiple versions. This issue resides within the HTCP (Hierarchical Timeout Control Protocol) handling mechanism, specifically in the htcpHandleTstRequest function that processes incoming HTCP packets. The vulnerability manifests when the daemon receives specially crafted packets designed to trigger a NULL pointer dereference condition, ultimately leading to complete daemon crash and service disruption. The affected versions include Squid 2.x prior to 2.6.STABLE24 and 2.7 prior to 2.7.STABLE8, as well as Squid 3.0 prior to 3.0.STABLE24, indicating this flaw persisted across major Squid release lines for an extended period. The HTCP protocol serves as a mechanism for proxy servers to communicate with each other regarding cache behavior and timeout management, making this vulnerability particularly dangerous as it targets core communication functions.
The technical exploitation of this vulnerability occurs through the manipulation of HTCP packet structures sent to the designated HTCP port, typically configured to operate on port 4827. When the htcpHandleTstRequest function processes these malformed packets, it fails to properly validate incoming data structures, specifically neglecting to check for NULL pointer conditions before dereferencing pointers within the packet handling logic. This lack of input validation creates a predictable crash scenario where the daemon attempts to access memory locations that have not been properly initialized, resulting in segmentation faults and subsequent process termination. The flaw aligns with CWE-476 which specifically addresses NULL pointer dereference vulnerabilities, representing a fundamental weakness in memory management and input validation practices within the Squid codebase. From an operational perspective, this vulnerability enables remote attackers to execute a simple yet effective denial of service attack against Squid proxy servers without requiring authentication or special privileges.
The operational impact of CVE-2010-0639 extends beyond simple service disruption, potentially affecting entire network infrastructures that depend on Squid for caching and proxy services. Organizations utilizing Squid as a core component of their network infrastructure could experience significant downtime, particularly in environments where proxy caching is critical for bandwidth optimization and content filtering. The vulnerability's remote exploitability means that attackers can initiate attacks from any location on the internet, making it particularly dangerous for publicly accessible proxy servers. From an adversarial perspective, this flaw fits well within the ATT&CK framework under the T1499.004 technique category, which covers "Endpoint Denial of Service" through the exploitation of software vulnerabilities. The attack vector specifically targets network services and can be automated, making it a preferred method for attackers seeking to disrupt services without detection. Network administrators and security professionals must consider the broader implications of such vulnerabilities, as they often serve as entry points for more sophisticated attacks or can be combined with other exploits to create more comprehensive compromise scenarios.
Mitigation strategies for CVE-2010-0639 primarily involve immediate patching of affected Squid installations to the recommended stable versions that contain the necessary code fixes. The vulnerability can be addressed through the implementation of network-level access controls that restrict HTCP port access to trusted networks only, effectively reducing the attack surface. Additionally, monitoring for unusual traffic patterns on the HTCP port and implementing intrusion detection systems can help identify exploitation attempts. Organizations should also consider disabling HTCP functionality entirely if it is not required for their specific use cases, as this removes the attack vector completely. From a defensive standpoint, the vulnerability demonstrates the importance of proper input validation and error handling in network services, particularly those handling external communications. Security teams should implement regular vulnerability assessments and maintain updated threat intelligence to identify similar patterns in other software components that might present analogous weaknesses requiring similar mitigation approaches.