CVE-2016-5386 in Google
Summary
by MITRE
The net/http package in Go through 1.6 does not attempt to address RFC 3875 section 4.1.18 namespace conflicts and therefore does not protect CGI applications from the presence of untrusted client data in the HTTP_PROXY environment variable, which might allow remote attackers to redirect a CGI application's outbound HTTP traffic to an arbitrary proxy server via a crafted Proxy header in an HTTP request, aka an "httpoxy" issue.
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Analysis
by VulDB Data Team • 09/05/2022
The CVE-2016-5386 vulnerability represents a critical security flaw in the Go programming language's net/http package affecting versions through 1.6. This issue stems from the improper handling of HTTP proxy configurations within CGI applications, creating a significant attack vector for remote adversaries. The vulnerability specifically targets the failure to properly address namespace conflicts as outlined in RFC 3875 section 4.1.18, which governs the interaction between HTTP headers and environment variables in CGI environments. When a CGI application processes HTTP requests, it typically relies on environment variables to determine proxy settings, making the application susceptible to manipulation through crafted HTTP headers.
The technical flaw manifests when an attacker crafts a malicious Proxy header in an HTTP request that gets processed by the vulnerable Go application. This header manipulation allows attackers to inject untrusted data into the HTTP_PROXY environment variable, which the application then uses to configure outbound HTTP traffic. The vulnerability essentially enables a man-in-the-middle attack scenario where the CGI application's network requests are redirected through an attacker-controlled proxy server instead of the intended destination. This occurs because the Go runtime fails to sanitize or validate the Proxy header contents before incorporating them into the application's environment variables, creating a direct path for traffic redirection attacks.
The operational impact of this vulnerability extends beyond simple traffic redirection, as it can enable sophisticated attack chains including credential theft, data exfiltration, and service disruption. Attackers can leverage this vulnerability to intercept sensitive information flowing through CGI applications, particularly in environments where applications make outbound requests to external services or APIs. The vulnerability affects web applications built with Go that utilize CGI interfaces, potentially compromising entire application stacks that rely on proper proxy handling for external communications. This issue particularly impacts enterprise web applications, content management systems, and any CGI-based services that process user input through HTTP headers without proper validation mechanisms.
Organizations should implement immediate mitigations including updating to Go versions 1.7 or later where the vulnerability has been addressed, implementing proxy header validation at the application level, and configuring proper network segmentation to limit the impact of potential proxy redirection attacks. The vulnerability aligns with CWE-20, "Improper Input Validation," and represents a specific implementation weakness in environment variable handling within web frameworks. From an ATT&CK perspective, this vulnerability maps to T1071.004, "Application Layer Protocol: DNS," and T1041, "Exfiltration Over C2 Channel," as attackers can use the compromised proxy configuration to establish unauthorized communication channels. Additionally, the issue demonstrates the importance of proper input sanitization and environment variable management in web application security, emphasizing the need for comprehensive security testing of HTTP request processing components within server-side applications.