CVE-2018-18358 in Chrome
Summary
by MITRE
Lack of special casing of localhost in WPAD files in Google Chrome prior to 71.0.3578.80 allowed an attacker on the local network segment to proxy resources on localhost via a crafted WPAD file.
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Analysis
by VulDB Data Team • 08/01/2024
This vulnerability resides in the handling of Web Proxy Auto-Discovery protocol files within Google Chrome browsers prior to version 71.0.3578.80. The issue stems from insufficient validation of localhost addresses in WPAD configuration files, creating a security gap that allows attackers to manipulate proxy settings for local network resources. The vulnerability is categorized under CWE-264, which addresses permissions, privileges, and access control weaknesses, specifically manifesting in improper handling of network proxy configurations.
The technical flaw occurs when Chrome processes WPAD files that contain localhost references without proper validation of the local network context. When a malicious actor successfully places a crafted WPAD file on the local network segment, the browser accepts proxy instructions that redirect localhost traffic through the attacker-controlled proxy server. This allows the attacker to intercept, modify, or redirect traffic intended for local services, effectively bypassing normal security boundaries that should protect localhost resources. The vulnerability exploits the trust relationship between the browser and local network proxy configuration mechanisms.
The operational impact of this vulnerability is significant as it enables man-in-the-middle attacks within local network segments where attackers can intercept sensitive localhost communications. This includes access to local web servers, development environments, and internal services that typically should remain isolated from external network access. Attackers can leverage this to capture authentication credentials, exfiltrate sensitive data, or inject malicious content into local applications. The attack vector requires only network access to the local segment, making it particularly dangerous in corporate environments where localhost services often contain sensitive information.
Mitigation strategies should focus on updating Chrome browsers to version 71.0.3578.80 or later, which implements proper localhost validation in WPAD file processing. Network administrators should also implement network segmentation and monitoring to detect unusual proxy configuration changes. Additionally, organizations should consider disabling automatic WPAD discovery where possible and implementing strict access controls for localhost services. This vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol: DNS, as it involves manipulation of network proxy configurations to redirect traffic. The fix implemented by Google addresses the root cause by ensuring that localhost references in WPAD files are properly validated against the local network context, preventing unauthorized proxy redirection of local resources.