CVE-2016-3213 in Internet Explorer
Summary
by MITRE
The Web Proxy Auto Discovery (WPAD) protocol implementation in Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT 8.1, Windows 10 Gold and 1511, and Internet Explorer 9 through 11 has an improper fallback mechanism, which allows remote attackers to gain privileges via NetBIOS name responses, aka "WPAD Elevation of Privilege Vulnerability."
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Analysis
by VulDB Data Team • 08/24/2022
The CVE-2016-3213 vulnerability represents a critical privilege escalation flaw within the Web Proxy Auto Discovery protocol implementation across multiple Microsoft Windows operating systems and Internet Explorer versions. This vulnerability stems from an improper fallback mechanism in the WPAD protocol that was designed to automatically configure web proxy settings for network clients. The protocol operates by allowing systems to discover proxy configuration information through various methods including DNS resolution and NetBIOS name resolution. When a system attempts to locate a proxy configuration file, it first tries DNS resolution and falls back to NetBIOS name resolution if DNS fails. The flaw occurs in how this fallback process handles NetBIOS responses, creating a window of opportunity for malicious actors to manipulate the proxy configuration discovery process.
The technical exploitation of this vulnerability relies on the attacker's ability to respond to NetBIOS name queries with malicious proxy configuration files. When a Windows system attempts to configure its proxy settings and fails to resolve the proxy configuration through DNS, it falls back to NetBIOS name resolution which can be manipulated by an attacker on the local network. This creates a scenario where an attacker can respond to NetBIOS queries and provide a malicious proxy.pac file that can execute arbitrary code or redirect traffic to malicious endpoints. The vulnerability specifically affects systems running Windows Vista SP2 through Windows 10 version 1511, along with Internet Explorer 9 through 11, making it particularly widespread across enterprise environments. This flaw aligns with CWE-200, which addresses improper output neutralization for logs, and more specifically relates to CWE-264, which covers permissions, privileges, and access control issues.
The operational impact of CVE-2016-3213 extends beyond simple privilege escalation to encompass significant network security implications. Attackers can leverage this vulnerability to gain elevated privileges on affected systems, potentially allowing them to execute arbitrary code with system-level privileges. The attack vector requires network access to the local network segment where the target system resides, making it particularly dangerous in corporate environments where attackers might gain access through compromised endpoints or by positioning themselves on the same network segment. This vulnerability can enable attackers to conduct man-in-the-middle attacks, redirect traffic to malicious servers, or execute code on target systems without requiring user interaction. The impact is amplified in environments where users frequently connect to public or untrusted networks, as the attack can be executed simply by being on the same local network segment.
Organizations affected by CVE-2016-3213 should implement immediate mitigations to address the vulnerability. Microsoft released security updates that addressed this issue by modifying the WPAD fallback mechanism to prevent malicious NetBIOS responses from being accepted as valid proxy configuration files. The recommended mitigation involves applying the appropriate security patches from Microsoft as soon as possible, which can be obtained through Windows Update or Microsoft Update Catalog. Network administrators should also consider implementing additional security measures such as disabling WPAD functionality where possible, configuring secure proxy settings through group policies, and monitoring network traffic for suspicious NetBIOS name resolution activities. According to ATT&CK framework, this vulnerability maps to T1068, which covers 'Exploitation for Privilege Escalation', and T1566, which covers 'Phishing for Information', as attackers may use this vulnerability as part of broader attack campaigns to establish persistent access and escalate privileges within compromised networks. Organizations should also consider network segmentation to limit the potential impact of such attacks and implement intrusion detection systems to monitor for suspicious NetBIOS traffic patterns that may indicate exploitation attempts.