CVE-2007-1560 in Squid
Summary
by MITRE
The clientProcessRequest() function in src/client_side.c in Squid 2.6 before 2.6.STABLE12 allows remote attackers to cause a denial of service (daemon crash) via crafted TRACE requests that trigger an assertion error.
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Analysis
by VulDB Data Team • 06/09/2025
The vulnerability identified as CVE-2007-1560 represents a critical denial of service flaw within the Squid web proxy software ecosystem. This issue affects Squid versions prior to 2.6.STABLE12 and specifically targets the clientProcessRequest() function located in the src/client_side.c source file. The vulnerability manifests when the proxy daemon receives specially crafted TRACE HTTP requests that are designed to trigger an assertion error within the software's processing logic. Such assertion failures typically occur when the software encounters unexpected conditions that violate its internal assumptions about valid input parameters or processing states.
The technical exploitation of this vulnerability demonstrates a classic buffer over-read or logic error condition that occurs during HTTP request parsing and processing. When a remote attacker crafts a TRACE request with specific parameters that cause the clientProcessRequest() function to encounter an unexpected state, the software's assertion mechanism triggers and terminates the daemon process. This behavior aligns with CWE-248, which addresses the exposure of an exception or assertion error that results in a program crash or termination. The flaw essentially creates a condition where legitimate network traffic can be used to intentionally destabilize the proxy service, causing it to become unresponsive and requiring manual intervention or system restart to restore functionality.
The operational impact of this vulnerability extends beyond simple service disruption, as it represents a potential vector for coordinated attacks against proxy infrastructure that could lead to widespread availability issues. Organizations relying on Squid as their primary web proxy solution face significant risk when exposed to this vulnerability, particularly in environments where proxy services are critical to network operations. The attack vector is particularly concerning because TRACE requests are legitimate HTTP methods that may be processed by various network components, making this vulnerability difficult to detect and filter at the network level. From an attacker's perspective, this represents a low-effort, high-impact method for causing service disruption without requiring advanced exploitation techniques or privileged access.
Mitigation strategies for this vulnerability center on immediate patch application to upgrade to Squid 2.6.STABLE12 or later versions where the assertion error has been properly addressed. Network administrators should also implement defensive measures such as configuring proxy servers to reject TRACE requests entirely, as these requests are typically unnecessary for proxy operations and provide no functional benefit. Additionally, monitoring systems should be configured to detect unusual daemon crash patterns that may indicate exploitation attempts. This vulnerability demonstrates the importance of proper input validation and error handling in network services, aligning with ATT&CK technique T1499.004 for network denial of service attacks. Organizations should also consider implementing intrusion detection systems that can identify and block malformed TRACE requests that match known attack patterns, providing an additional layer of defense against this specific class of vulnerability. The incident underscores the critical need for regular security patch management and proper software lifecycle maintenance to prevent exploitation of known vulnerabilities that can cause significant operational disruption.