CVE-2016-4054 in Squid
Summary
by MITRE
Buffer overflow in Squid 3.x before 3.5.17 and 4.x before 4.0.9 allows remote attackers to 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-2016-4054 represents a critical buffer overflow flaw within the Squid caching proxy software that affects versions prior to 3.5.17 and 4.0.9. This security issue specifically targets the handling of Edge Side Includes (ESI) responses, which are fragments of HTML content that can be dynamically assembled by the proxy server. The flaw occurs when Squid processes ESI responses that contain crafted malicious data, leading to memory corruption that can be exploited by remote attackers to execute arbitrary code on the affected system. The vulnerability stems from insufficient input validation and bounds checking within the ESI processing module, creating an opportunity for attackers to overwrite adjacent memory locations with malicious payloads.
The technical implementation of this buffer overflow exploit involves manipulating ESI elements within HTTP responses that pass through the Squid proxy. When the proxy encounters specially crafted ESI tags containing oversized data or malformed structures, the memory allocation routines fail to properly validate the input size, resulting in buffer overrun conditions. This memory corruption can potentially overwrite critical program variables, return addresses, or function pointers, allowing attackers to redirect execution flow and inject malicious code. The vulnerability is particularly concerning because it operates at the application layer and can be triggered through normal web traffic without requiring authentication or specialized privileges. The flaw aligns with CWE-121, which describes heap-based buffer overflow conditions, and represents a classic example of how improper input handling can lead to arbitrary code execution.
The operational impact of CVE-2016-4054 extends beyond simple code execution, as it can enable attackers to compromise entire proxy infrastructure and potentially escalate privileges within the network environment. Organizations relying on Squid as a caching or filtering proxy server face significant risk since the vulnerability can be exploited remotely through standard HTTP traffic. Successful exploitation could allow attackers to gain full control over the proxy server, potentially leading to man-in-the-middle attacks, data exfiltration, or use of the compromised proxy as a pivot point for attacking internal network resources. The attack vector is particularly dangerous because it can be executed against any system running vulnerable Squid versions without requiring direct access to the target network. This vulnerability maps to several ATT&CK techniques including T1059 for command and script execution, T1071 for application layer protocol usage, and T1566 for credential harvesting through proxy manipulation.
Organizations should immediately implement mitigations including updating to patched versions of Squid software, specifically versions 3.5.17 or 4.0.9 and later, which contain proper bounds checking and input validation for ESI processing. Additional defensive measures include configuring Squid to disable ESI processing entirely if not required for business operations, implementing network segmentation to limit exposure, and monitoring for unusual traffic patterns that might indicate exploitation attempts. Security teams should also consider implementing intrusion detection systems with signatures specifically targeting ESI-related attack patterns and conducting regular vulnerability assessments to identify any remaining instances of vulnerable Squid installations. The remediation process should include thorough testing of updated configurations to ensure that legitimate ESI functionality remains intact while eliminating the security risk. Organizations should also review their proxy server configurations to minimize attack surface and implement proper access controls to limit potential exploitation avenues.