CVE-2015-4334 in ProxySG
Summary
by MITRE
The default configuration of SGOS in Blue Coat ProxySG before 6.2.16.5, 6.5 before 6.5.7.1, and 6.6 before 6.6.2.1 forwards authentication challenges from upstream origin content servers (OCS) when used in an explicit proxy deployment, which makes it easier for remote attackers to obtain sensitive information via a 407 (aka Proxy Authentication Required) HTTP status code, as demonstrated when using NTLM authentication.
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Analysis
by VulDB Data Team • 11/24/2024
The vulnerability described in CVE-2015-4334 represents a critical configuration flaw in the Blue Coat ProxySG software that affects multiple version ranges including pre-6.2.16.5, pre-6.5.7.1, and pre-6.6.2.1 releases. This issue specifically impacts explicit proxy deployments where the system fails to properly handle authentication challenges from upstream origin content servers. The flaw stems from the default configuration's tendency to forward authentication challenges rather than properly intercept and manage them, creating an unintended information disclosure channel that significantly weakens the security posture of the proxy infrastructure.
The technical mechanism behind this vulnerability involves the improper handling of HTTP 407 Proxy Authentication Required status codes when NTLM authentication is employed. When upstream servers issue these authentication challenges, the affected ProxySG appliances forward them to clients instead of processing them internally or blocking them appropriately. This behavior creates a scenario where remote attackers can observe and exploit the authentication flow to gather sensitive information about the network infrastructure and authentication mechanisms in use. The vulnerability specifically targets the interaction between the proxy server and origin content servers, where the proxy fails to act as a proper intermediary in the authentication process.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with actionable intelligence about the authentication infrastructure and potentially enables more sophisticated attacks. By observing the 407 status codes and associated authentication challenges, attackers can map out the authentication mechanisms used within the network, identify the presence of specific authentication protocols, and potentially exploit this knowledge to conduct credential harvesting attacks or bypass authentication controls. This vulnerability particularly affects environments that rely on NTLM authentication, which is commonly used in enterprise environments with active directory integration, making the information disclosure particularly valuable to threat actors.
The vulnerability aligns with CWE-200 (Information Exposure) and CWE-312 (Sensitive Data Exposure) categories, as it exposes authentication-related information to unauthorized parties. From an ATT&CK framework perspective, this vulnerability maps to T1566 (Phishing) and T1552 (Unsecured Credentials) techniques, as it enables attackers to gather information that can be used to craft more effective credential theft attacks. The exposure of authentication challenges also relates to T1071.004 (Application Layer Protocol: DNS) and T1046 (Network Service Scanning) as attackers can use this information to better understand network services and protocols in use. Organizations using affected ProxySG versions face increased risk of credential compromise and network reconnaissance activities.
Mitigation strategies for CVE-2015-4334 require immediate implementation of configuration changes to ensure proper handling of authentication challenges from upstream servers. The primary solution involves updating to the patched versions mentioned in the CVE description, specifically versions 6.2.16.5, 6.5.7.1, and 6.6.2.1, which contain the necessary fixes to prevent forwarding of authentication challenges. Additionally, administrators should review and modify proxy configuration settings to ensure that authentication challenges are properly intercepted and managed rather than forwarded to client systems. Network segmentation and access controls should be implemented to limit the impact of any potential exploitation, and monitoring should be enhanced to detect unusual patterns of authentication challenge forwarding or unauthorized access attempts. Regular security assessments and vulnerability scanning should be conducted to identify any other misconfigurations that could potentially expose similar information disclosure vulnerabilities in the network infrastructure.