CVE-2016-4052 in Squid
Summary
by MITRE
Multiple stack-based buffer overflows in Squid 3.x before 3.5.17 and 4.x before 4.0.9 allow remote HTTP servers to cause a denial of service or execute arbitrary code via crafted Edge Side Includes (ESI) responses.
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Analysis
by VulDB Data Team • 10/21/2018
The vulnerability identified as CVE-2016-4052 represents a critical stack-based buffer overflow flaw affecting Squid proxy software versions 3.x prior to 3.5.17 and 4.x prior to 4.0.9. This vulnerability specifically targets the Edge Side Includes (ESI) processing functionality within Squid, which is designed to handle dynamic content inclusion in web responses. The flaw arises from insufficient input validation when processing ESI directives, creating opportunities for remote attackers to exploit memory corruption issues through specially crafted HTTP responses. The vulnerability falls under CWE-121 Stack-based Buffer Overflow, which is classified as a fundamental memory safety issue that can lead to arbitrary code execution or system crashes.
The technical exploitation of this vulnerability occurs when Squid receives HTTP responses containing malformed ESI directives that trigger buffer overflow conditions during parsing operations. The stack-based nature of the overflow means that attacker-controlled data can overwrite adjacent memory locations including return addresses and function pointers, potentially allowing remote code execution. Attackers can craft malicious HTTP responses that contain oversized ESI elements or malformed directives, which when processed by the vulnerable Squid proxy server, cause the application to crash or execute unintended code. This type of vulnerability is particularly dangerous in proxy environments where Squid servers handle traffic from multiple sources and users, as it can be leveraged for both denial of service attacks and persistent code execution.
The operational impact of CVE-2016-4052 extends beyond simple service disruption, as it can enable complete system compromise when exploited successfully. Organizations using vulnerable Squid versions face significant risk of unauthorized access to their network infrastructure, as the vulnerability can be exploited remotely without authentication. The vulnerability affects both Squid 3.x and 4.x major versions, indicating a widespread issue across multiple release lines that required immediate patching. The exploitability of this vulnerability aligns with ATT&CK technique T1210, which covers exploitation of remote services through memory corruption vulnerabilities, making it a preferred target for attackers seeking to gain persistent access to network infrastructure. The denial of service aspect of the vulnerability can be used to disrupt legitimate services, while the code execution capability enables more sophisticated attacks including lateral movement and data exfiltration.
Organizations should prioritize immediate patching of all affected Squid installations to mitigate this vulnerability, as the security advisory for CVE-2016-4052 was released well before the end of the software support lifecycle for affected versions. The recommended mitigation strategy involves upgrading to Squid versions 3.5.17 or 4.0.9, which contain the necessary fixes to prevent the buffer overflow conditions. Network administrators should also implement monitoring for suspicious HTTP traffic patterns that might indicate exploitation attempts, particularly around ESI processing functionality. Additional defensive measures include restricting ESI processing capabilities where possible, implementing proper input validation for HTTP responses, and deploying intrusion detection systems that can identify malformed ESI content. The vulnerability demonstrates the critical importance of regular security updates and proper input validation in proxy server implementations, as it represents a classic example of how insufficient bounds checking in application code can lead to severe security consequences.