CVE-2016-2571 in Squid
Summary
by MITRE
http.cc in Squid 3.x before 3.5.15 and 4.x before 4.0.7 proceeds with the storage of certain data after a response-parsing failure, which allows remote HTTP servers to cause a denial of service (assertion failure and daemon exit) via a malformed response.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/08/2022
The vulnerability identified as CVE-2016-2571 represents a critical flaw in the Squid proxy server software that affects versions prior to 3.5.15 and 4.0.7. This issue resides within the http.cc component of the Squid HTTP implementation and demonstrates a classic example of improper error handling that can be exploited to cause remote denial of service conditions. The vulnerability specifically targets the response parsing mechanism where the software fails to properly validate or reject malformed HTTP responses before proceeding with data storage operations, creating a scenario where malicious HTTP servers can manipulate the proxy behavior through crafted responses.
The technical exploitation of this vulnerability occurs when Squid receives an HTTP response that contains malformed data during the parsing process. Rather than gracefully handling this parsing failure and rejecting the malformed content, the software continues to process and store the corrupted data segments. This continuation leads to assertion failures within the proxy daemon, ultimately causing the Squid service to terminate unexpectedly. The flaw stems from a lack of proper input validation and error recovery mechanisms within the HTTP response handling code, allowing attackers to craft specific HTTP responses that trigger the assertion failure condition. This behavior aligns with CWE-248, which addresses the issue of an exception being thrown for an unspecified error condition, and demonstrates how improper error handling can lead to system instability and denial of service.
The operational impact of CVE-2016-2571 extends beyond simple service disruption, as it can affect organizations relying on Squid as a critical infrastructure component for web filtering, caching, or proxy services. When exploited, the vulnerability can cause cascading failures in environments where Squid serves as a primary HTTP proxy, potentially affecting thousands of users or applications dependent on the proxy infrastructure. The daemon exit creates a service interruption that requires manual intervention to restore normal operations, resulting in both immediate availability issues and potential business continuity concerns. This vulnerability particularly affects organizations using Squid in enterprise environments where proxy services are essential for network traffic management and security policy enforcement.
Mitigation strategies for CVE-2016-2571 focus primarily on immediate software upgrades to patched versions of Squid that address the flawed response parsing logic. Organizations should prioritize updating their Squid installations to versions 3.5.15 or 4.0.7 and later, which contain the necessary code modifications to properly handle malformed HTTP responses. Additionally, network administrators should implement monitoring solutions to detect unusual daemon exit patterns or assertion failures that may indicate exploitation attempts. The vulnerability can also be mitigated through network-level controls such as implementing strict HTTP response validation at network boundaries or deploying intrusion detection systems that can identify and block malicious HTTP responses designed to trigger this specific flaw. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service, and organizations should consider implementing defensive measures against this specific attack vector through proper patch management and network segmentation strategies.