CVE-2016-4554 in Squid
Summary
by MITRE
mime_header.cc in Squid before 3.5.18 allows remote attackers to bypass intended same-origin restrictions and possibly conduct cache-poisoning attacks via a crated HTTP Host header, aka a "header smuggling" issue.
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Analysis
by VulDB Data Team • 08/18/2022
The vulnerability identified as CVE-2016-4554 represents a critical security flaw in the Squid proxy server software that affects versions prior to 3.5.18. This issue resides within the mime_header.cc component and specifically targets the HTTP Host header handling mechanism. The vulnerability enables remote attackers to manipulate the header parsing process in a manner that can circumvent the intended same-origin restrictions that are fundamental to web security protocols. The flaw manifests when the proxy server processes crafted HTTP Host headers that contain carriage return characters, allowing malicious actors to inject additional headers that should not be permitted in the request chain.
The technical implementation of this vulnerability stems from inadequate input validation and header parsing within Squid's MIME header processing subsystem. When the proxy server encounters a Host header containing embedded carriage return sequences, it fails to properly sanitize or reject these malformed inputs. This parsing failure creates a condition where attackers can smuggle additional HTTP headers into the request stream, effectively bypassing the normal security boundaries that separate different origins and domains. The vulnerability is classified as a header smuggling attack pattern that leverages the HTTP protocol's flexibility in header field parsing and the proxy server's insufficient validation mechanisms.
The operational impact of CVE-2016-4554 extends beyond simple bypass of access controls to potentially enable cache poisoning attacks that can have severe consequences for web infrastructure security. When successful, this vulnerability allows attackers to inject malicious content into Squid's cache storage, affecting all users who subsequently access the cached content. The cache poisoning aspect means that legitimate web resources can be replaced with malicious payloads, creating a persistent threat that can affect multiple users over extended periods. This capability undermines the fundamental trust model of proxy servers and can lead to man-in-the-middle attacks, data exfiltration, and the compromise of user sessions.
Organizations utilizing Squid proxy servers in their infrastructure should consider immediate remediation through patching to version 3.5.18 or later, which contains the necessary fixes for this vulnerability. The mitigation strategy should also include monitoring for anomalous HTTP header patterns and implementing additional network-level controls to detect and prevent header smuggling attempts. Security teams should also consider deploying web application firewalls that can detect and block malformed HTTP headers that may indicate exploitation attempts. This vulnerability aligns with CWE-129, which addresses improper handling of input boundaries, and maps to ATT&CK technique T1071.004 for application layer protocol manipulation. The flaw demonstrates the critical importance of proper input validation and sanitization in network security appliances, particularly those handling HTTP traffic where header manipulation can have cascading security implications throughout the entire web infrastructure stack.