CVE-2016-2570 in Squid
Summary
by MITRE
The Edge Side Includes (ESI) parser in Squid 3.x before 3.5.15 and 4.x before 4.0.7 does not check buffer limits during XML parsing, which allows remote HTTP servers to cause a denial of service (assertion failure and daemon exit) via a crafted XML document, related to esi/CustomParser.cc and esi/CustomParser.h.
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Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2016-2570 represents a critical buffer overflow condition within the Edge Side Includes (ESI) parser component of Squid proxy software. This flaw exists in versions 3.x prior to 3.5.15 and 4.x prior to 4.0.7, affecting a significant portion of the Squid proxy server installations that rely on ESI processing for dynamic content inclusion. The issue stems from insufficient input validation during XML parsing operations, creating a scenario where maliciously crafted XML documents can trigger unexpected behavior in the application's memory management systems.
The technical implementation of this vulnerability occurs within the esi/CustomParser.cc and esi/CustomParser.h source files, where the ESI parser fails to enforce proper buffer size limitations during XML document processing. When a remote HTTP server delivers a specially crafted XML payload to a vulnerable Squid instance, the parser attempts to process the malformed data without adequate boundary checks, leading to memory corruption conditions. This specific failure mode manifests as assertion failures that ultimately cause the Squid daemon to terminate unexpectedly, resulting in a complete denial of service condition that affects all proxy services until manual restart occurs.
The operational impact of this vulnerability extends beyond simple service disruption, as it provides attackers with a reliable method to compromise proxy infrastructure without requiring authentication or elevated privileges. The vulnerability can be exploited through standard HTTP requests containing malicious XML content, making it particularly dangerous in environments where Squid serves as a critical network component for content filtering, caching, or web proxy services. Organizations relying on Squid for enterprise proxy services face significant risk of service interruptions that can cascade into broader network availability issues, especially in scenarios where multiple proxy servers are configured to handle similar traffic loads.
From a cybersecurity perspective, this vulnerability aligns with CWE-129, which addresses insufficient input validation, and demonstrates characteristics consistent with ATT&CK technique T1499.004 related to network denial of service. The flaw represents a classic buffer overflow condition that exploits the lack of proper bounds checking in XML parsing libraries, making it particularly susceptible to exploitation by threat actors seeking to disrupt network services. Organizations should prioritize immediate patching of affected Squid installations and implement network monitoring to detect potential exploitation attempts. Additional mitigations include configuring Squid to disable ESI processing when not required, implementing rate limiting for XML content processing, and establishing automated alerting for daemon termination events that could indicate exploitation attempts.
The vulnerability underscores the importance of proper input validation in parsing libraries and highlights the critical need for memory safety practices in network infrastructure software. Given the widespread use of Squid across enterprise and organizational networks, the impact of this flaw extends beyond individual systems to potentially affect entire network infrastructures. Security teams should conduct comprehensive vulnerability assessments to identify all instances of affected Squid versions and ensure that proper network segmentation prevents unauthorized access to proxy services that might be exploited for broader attack vectors.