CVE-2015-0881 in Squid
Summary
by MITRE
CRLF injection vulnerability in Squid before 3.1.1 allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via a crafted header in a response.
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Analysis
by VulDB Data Team • 03/10/2022
The CVE-2015-0881 vulnerability represents a critical CRLF injection flaw in the Squid proxy server software affecting versions prior to 3.1.1. This vulnerability stems from insufficient input validation and sanitization within the HTTP header processing mechanisms of the proxy server. The flaw enables remote attackers to inject carriage return line feed sequences into HTTP responses, which can be exploited to manipulate the HTTP protocol behavior in dangerous ways. The vulnerability specifically manifests when the proxy server processes crafted headers in HTTP responses, allowing attackers to insert malicious content that can be interpreted by downstream systems as legitimate HTTP headers.
The technical exploitation of this vulnerability leverages the fundamental weakness in how Squid handles header data during the proxy processing phase. When a malicious actor crafts a specially formatted HTTP header containing CRLF sequences, the proxy server fails to properly sanitize this input before forwarding it to the client or upstream servers. This creates a condition where the injected sequences can cause the HTTP response to be split into multiple responses, enabling attackers to inject arbitrary HTTP headers into the response stream. The vulnerability operates at the application layer and can be triggered through various HTTP methods including GET, POST, and other request types that involve header processing within the proxy infrastructure.
The operational impact of CVE-2015-0881 extends beyond simple header injection, as it enables sophisticated HTTP response splitting attacks that can lead to session hijacking, cache poisoning, and cross-site scripting exploitation. Attackers can leverage this vulnerability to manipulate web application behavior by injecting malicious headers that alter the intended response structure. This can result in unauthorized access to protected resources, data leakage, or redirection to malicious content. The vulnerability particularly affects web applications that rely on Squid as a proxy server for content filtering, caching, or security enforcement. The attack surface is broad as it can affect any HTTP traffic passing through the vulnerable proxy server, potentially compromising entire web infrastructures that depend on Squid for traffic management.
Organizations implementing mitigations for this vulnerability should prioritize immediate patching of Squid installations to version 3.1.1 or later, which contains the necessary input validation fixes. Network administrators should also implement additional security controls including HTTP header filtering, proxy server configuration hardening, and monitoring for suspicious header patterns. The vulnerability aligns with CWE-1107, which addresses improper neutralization of CRLF sequences in HTTP headers, and maps to ATT&CK technique T1190 for exploitation of remote services. Security teams should conduct thorough vulnerability assessments to identify all systems running vulnerable Squid versions and implement network segmentation to limit potential attack vectors. Regular security audits and monitoring of proxy server logs can help detect exploitation attempts and provide early warning of potential compromises.