CVE-2006-6982 in 3proxy
Summary
by MITRE
3proxy 0.5 to 0.5.2 does not offer NTLM authentication before basic authentication, which might cause browsers with incomplete RFC2616/RFC2617 support to use basic cleartext authentication even if NTLM is available, which makes it easier for attackers to steal credentials.
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Analysis
by VulDB Data Team • 08/19/2018
The vulnerability described in CVE-2006-6982 affects 3proxy versions 0.5 through 0.5.2 and represents a critical flaw in the proxy server's authentication mechanism. This issue stems from the proxy's failure to properly implement the authentication negotiation process as defined in the relevant internet standards. The vulnerability specifically impacts how the proxy server handles authentication requests from client browsers, creating a scenario where security mechanisms can be bypassed through improper protocol handling.
The technical flaw manifests in the proxy server's authentication sequence where NTLM authentication is not offered as the primary authentication method before falling back to basic authentication. According to RFC 2616 and RFC 2617, proper HTTP authentication negotiation should prioritize stronger authentication mechanisms like NTLM over weaker ones such as basic authentication. When a client browser connects to the proxy server, it should first attempt NTLM authentication if supported, but the flawed 3proxy implementation fails to present this option, forcing browsers to proceed with basic authentication which transmits credentials in cleartext form.
This vulnerability creates significant operational impact for organizations using 3proxy as a web proxy solution. The flaw allows attackers to exploit the incomplete RFC compliance by intercepting authentication exchanges and capturing cleartext credentials that would otherwise be protected through NTLM authentication. The vulnerability is particularly dangerous because it leverages the behavior of browsers with incomplete RFC support, making it difficult for administrators to detect and prevent the exploitation. This issue directly relates to CWE-521 which addresses weak password reuse and CWE-312 which covers cleartext storage of sensitive information.
The attack vector for this vulnerability involves network traffic interception where attackers can capture authentication requests and responses. When browsers with incomplete RFC2616/RFC2617 support connect to the vulnerable proxy, they default to basic authentication even when NTLM capabilities exist. This behavior creates an authentication downgrade attack scenario where the security benefits of NTLM are bypassed, leaving credentials exposed to passive network monitoring. The vulnerability aligns with ATT&CK technique T1566 which covers phishing with social engineering and T1071 which covers application layer protocol usage, as it enables attackers to obtain credentials through compromised proxy communications.
Organizations should implement immediate mitigations including upgrading to a patched version of 3proxy that properly implements authentication negotiation according to RFC standards. The recommended approach involves ensuring that NTLM authentication is offered before basic authentication in the proxy configuration. Network administrators should also consider implementing additional security controls such as mandatory TLS encryption for proxy communications and monitoring for unusual authentication patterns that might indicate exploitation attempts. Regular security assessments should verify that proxy servers properly implement authentication mechanisms and that browsers are configured to use appropriate authentication methods. The vulnerability demonstrates the importance of adhering to established internet standards and proper protocol implementation to prevent security bypasses that can compromise authentication mechanisms.