CVE-2016-1000107 in Erlang
Summary
by MITRE
inets in Erlang possibly 22.1 and earlier follows RFC 3875 section 4.1.18 and therefore does not protect applications from the presence of untrusted client data in the HTTP_PROXY environment variable, which might allow remote attackers to redirect an 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 • 03/09/2024
The vulnerability identified as CVE-2016-1000107 affects the inets component of Erlang versions 22.1 and earlier, representing a critical security flaw that directly impacts web application security. This issue stems from the implementation's adherence to RFC 3875 section 4.1.18, which governs CGI environment variable handling. The flaw specifically manifests when applications process HTTP_PROXY environment variables without proper validation, creating a pathway for malicious actors to manipulate outbound network traffic. The vulnerability is categorized under CWE-284, which addresses improper access control, and more specifically aligns with CWE-94, representing improper control of generation of code, due to the potential for arbitrary code execution through proxy manipulation.
The technical implementation of this vulnerability occurs when an HTTP request contains a crafted Proxy header that gets processed by the inets component. This component, designed to handle HTTP communications, inadvertently propagates the Proxy header value into the HTTP_PROXY environment variable without sanitizing or validating the input data. When applications relying on this component make outbound HTTP requests, they may be redirected through an attacker-controlled proxy server specified in the malicious header. This behavior constitutes a man-in-the-middle attack vector where remote adversaries can intercept, modify, or redirect network traffic intended for legitimate destinations. The vulnerability operates at the application layer, affecting HTTP traffic flow and potentially exposing sensitive data to unauthorized parties.
The operational impact of this vulnerability extends beyond simple traffic redirection, as it can enable comprehensive network reconnaissance and data exfiltration attacks. An attacker exploiting this vulnerability can position themselves as an intermediary between the affected application and its intended network destinations, potentially capturing credentials, session tokens, or sensitive business data. The httpoxy attack pattern, which this vulnerability enables, has been documented in various security frameworks including the MITRE ATT&CK framework under the technique T1071.004 for application layer protocol traffic shaping. Organizations using Erlang-based applications that handle HTTP communications are particularly at risk, as the flaw affects core networking components rather than just specific application modules, making it challenging to isolate and remediate.
Mitigation strategies for this vulnerability require immediate attention and systematic implementation across affected systems. The most effective approach involves upgrading to Erlang versions that address this specific flaw, typically those beyond the 22.1 release. Organizations should also implement input validation mechanisms to sanitize Proxy headers before processing, ensuring that any environment variable modifications are properly validated against trusted proxy server configurations. Network-level protections such as firewall rules that block suspicious proxy header values and intrusion detection systems configured to detect anomalous HTTP traffic patterns can provide additional defense layers. Security teams should conduct comprehensive audits of all Erlang-based applications to identify potential exposure points and implement proper environment variable handling practices that prevent untrusted data from influencing proxy configuration. The vulnerability also underscores the importance of following security best practices such as the principle of least privilege and implementing secure coding guidelines that prevent environment variable manipulation in network communication components.