CVE-2016-4555 in Squid
Summary
by MITRE
client_side_request.cc in Squid 3.x before 3.5.18 and 4.x before 4.0.10 allows remote servers to cause a denial of service (crash) via crafted Edge Side Includes (ESI) responses.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 08/17/2022
The vulnerability identified as CVE-2016-4555 represents a critical denial of service flaw within the Squid caching proxy software that affects versions prior to 3.5.18 and 4.0.10. This vulnerability specifically targets the client_side_request.cc component of Squid's Edge Side Includes (ESI) processing functionality, creating a scenario where remote malicious servers can trigger unexpected crashes in the proxy system. The flaw exploits the way Squid handles ESI responses, which are used to dynamically include content from multiple sources within a single web page, making it particularly dangerous in environments where Squid serves as a gateway for complex web applications.
The technical implementation of this vulnerability stems from inadequate input validation within Squid's ESI processing logic. When Squid encounters crafted ESI responses from remote servers, the client_side_request.cc module fails to properly handle malformed or maliciously constructed ESI tags, leading to memory corruption or unexpected execution paths that ultimately result in application crashes. This behavior aligns with CWE-121, which categorizes heap-based buffer overflow conditions, and demonstrates how improper handling of external input can lead to system instability. The vulnerability operates at the application layer and can be exploited through network-based attacks without requiring authentication or specialized privileges.
The operational impact of CVE-2016-4555 extends beyond simple service disruption, potentially affecting the availability of critical web infrastructure that relies on Squid for caching and proxy services. Organizations using affected Squid versions may experience frequent service interruptions, particularly in high-traffic environments where ESI processing is commonly employed. The vulnerability can be exploited by attackers who control remote servers that deliver content to Squid caches, making it particularly concerning for enterprises that aggregate content from multiple sources or rely on third-party services. This flaw directly maps to the ATT&CK technique T1499.004, which describes network denial of service attacks, and represents a significant threat to business continuity and service availability in enterprise networks.
Mitigation strategies for this vulnerability require immediate patching of affected Squid installations to versions 3.5.18 or 4.0.10, which contain the necessary code modifications to properly validate ESI responses. Organizations should also implement network-level restrictions to limit ESI processing from untrusted sources, and consider disabling ESI functionality entirely if it is not required for specific use cases. Additional protective measures include monitoring for unusual crash patterns in proxy logs and implementing intrusion detection systems that can identify malicious ESI content patterns. Security teams should also conduct comprehensive vulnerability assessments to identify all systems running affected Squid versions and establish incident response procedures for handling similar vulnerabilities in the future.