CVE-2007-5355 in Web Proxy
Summary
by MITRE
The Web Proxy Auto-Discovery (WPAD) feature in Microsoft Internet Explorer 6 and 7, when a primary DNS suffix with three or more components is configured, resolves an unqualified wpad hostname in a second-level domain outside this configured DNS domain, which allows remote WPAD servers to conduct man-in-the-middle (MITM) attacks.
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Analysis
by VulDB Data Team • 06/02/2025
The vulnerability described in CVE-2007-5355 represents a critical flaw in Microsoft Internet Explorer's Web Proxy Auto-Discovery protocol implementation that fundamentally undermines network security assumptions. This weakness specifically affects Internet Explorer versions 6 and 7, where the browser's WPAD resolution mechanism exhibits improper DNS query behavior when systems are configured with primary DNS suffixes containing three or more components. The flaw creates a dangerous condition where the browser attempts to resolve unqualified hostnames through DNS queries that extend beyond the configured domain boundaries, thereby opening pathways for malicious actors to exploit.
The technical nature of this vulnerability stems from the improper handling of DNS resolution sequences within the WPAD protocol. When a system has a primary DNS suffix with multiple components such as company.subdomain.domain.com, Internet Explorer's WPAD resolution process fails to properly constrain DNS queries to the configured domain scope. Instead, it attempts to resolve the wpad hostname in a manner that allows queries to traverse into second-level domains outside the originally configured DNS namespace, creating an attack surface that adversaries can exploit. This behavior violates fundamental DNS security principles and demonstrates a clear failure in access control implementation.
The operational impact of this vulnerability is severe and directly enables man-in-the-middle attacks that can compromise network communications and data integrity. Attackers can deploy rogue WPAD servers within second-level domains that are accessible to the vulnerable systems, allowing them to intercept and manipulate web traffic passing through the compromised browsers. This capability extends beyond simple traffic interception to potentially enable credential theft, data exfiltration, and broader network infiltration. The vulnerability affects organizations that rely on Internet Explorer for web browsing and represents a significant risk to enterprise network security, particularly in environments where DNS suffix configuration follows common corporate naming conventions.
The weakness manifests as a specific implementation flaw in Microsoft's DNS resolution logic that can be categorized under CWE-20, which addresses "Improper Input Validation" and more specifically relates to improper DNS resolution behavior. From an ATT&CK framework perspective, this vulnerability maps to T1566.001 "Phishing by Email" and T1071.004 "Application Layer Protocol: DNS" as it enables attackers to manipulate DNS resolution results to redirect traffic. The vulnerability also connects to T1557.001 "Adversary-in-the-Middle: DNS Cache Poisoning" and T1046 "Network Service Scanning" as it provides a method for attackers to establish malicious proxy configurations. Organizations affected by this vulnerability face significant risk of unauthorized network access and data compromise, as the flaw allows remote attackers to establish persistent man-in-the-middle positions within the network infrastructure.
Mitigation strategies should focus on immediate remediation through Microsoft security updates and patches, while also implementing network-level controls to restrict DNS query behavior. Organizations should consider disabling WPAD functionality where possible and implementing proper DNS security measures including DNSSEC deployment. Network administrators should monitor for unauthorized DNS servers and implement proper access controls to prevent rogue WPAD server deployments. Additionally, security awareness training should emphasize the risks of visiting untrusted websites and the importance of maintaining up-to-date browser software to prevent exploitation of known vulnerabilities.