CVE-2016-4053 in Squid
Summary
by MITRE
Squid 3.x before 3.5.17 and 4.x before 4.0.9 allow remote attackers to obtain sensitive stack layout information via crafted Edge Side Includes (ESI) responses, related to incorrect use of assert and compiler optimization.
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Analysis
by VulDB Data Team • 10/21/2018
The vulnerability identified as CVE-2016-4053 affects Squid proxy servers version 3.x prior to 3.5.17 and 4.x prior to 4.0.9, presenting a significant information disclosure risk that can be exploited by remote attackers. This flaw specifically relates to the handling of Edge Side Includes (ESI) responses within the proxy server's processing pipeline. The vulnerability stems from improper implementation of assert statements combined with compiler optimization behaviors that can lead to predictable stack memory layouts being exposed to unauthorized parties.
The technical root cause of this vulnerability lies in the incorrect usage of assert macros within the Squid codebase when processing ESI responses. When assert statements are improperly implemented in conjunction with compiler optimizations, they can inadvertently leak stack memory layout information to remote attackers. This occurs because the assert mechanism, when compiled with optimization flags, may not properly handle memory alignment or stack frame management, resulting in sensitive information about the program's memory structure being exposed through crafted ESI responses. The vulnerability manifests when the proxy server processes specially crafted ESI content that triggers the problematic assert behavior, allowing attackers to gather information about the stack layout and potentially use this knowledge for further exploitation attempts.
From an operational perspective, this vulnerability represents a serious security concern for organizations relying on Squid as their primary proxy server solution. The information disclosure aspect can provide attackers with valuable insights into the target system's memory layout, which may subsequently be leveraged for more sophisticated attacks such as buffer overflow exploitation or other memory corruption techniques. The remote nature of the attack means that adversaries can exploit this vulnerability from outside the network perimeter without requiring physical access or prior authentication. The impact extends beyond simple information disclosure as the leaked stack information could potentially be used in conjunction with other vulnerabilities to achieve privilege escalation or system compromise.
Organizations should prioritize immediate remediation of this vulnerability by upgrading their Squid installations to versions 3.5.17 or 4.0.9, which contain the necessary fixes for the assert implementation issue. Additionally, security teams should implement network monitoring to detect potential exploitation attempts involving crafted ESI responses. The vulnerability aligns with CWE-200, which addresses improper information exposure, and can be categorized under ATT&CK technique T1059 for command and control communications. Network segmentation and firewall rules should be reviewed to limit unnecessary exposure of Squid servers to external traffic, while also ensuring that ESI processing capabilities are properly configured and restricted to trusted sources only. Regular security assessments should include verification of proper assert implementation and compiler optimization settings to prevent similar issues from emerging in other components of the infrastructure.