CVE-2018-6076 in Chrome
Summary
by MITRE
Insufficient encoding of URL fragment identifiers in Blink in Google Chrome prior to 65.0.3325.146 allowed a remote attacker to perform a DOM based XSS attack via a crafted HTML page.
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Analysis
by VulDB Data Team • 06/06/2023
The vulnerability identified as CVE-2018-6076 represents a critical security flaw in the Blink rendering engine that powers Google Chrome and other Chromium-based browsers. This issue specifically targets the handling of URL fragment identifiers, which are the portion of a URL that follows the hash symbol and typically used for client-side navigation within web pages. The vulnerability stems from insufficient encoding mechanisms that fail to properly sanitize fragment identifiers before processing them in the browser's DOM structure.
The technical flaw manifests when a malicious actor crafts a specially designed HTML page that contains a URL with a fragment identifier containing potentially harmful JavaScript code. When Chrome processes such a URL, the insufficient encoding allows the malicious content to bypass security checks and execute within the browser context. This creates a DOM-based cross-site scripting vulnerability where the attack vector operates entirely through the manipulation of the Document Object Model rather than traditional server-side input validation failures. The vulnerability is particularly dangerous because it can be triggered simply by visiting a malicious webpage, without requiring any user interaction beyond navigation.
From an operational perspective, this vulnerability presents significant risks to users who may unknowingly visit compromised websites or be redirected through malicious links. The attack can potentially lead to session hijacking, credential theft, data exfiltration, or the execution of arbitrary code on the victim's machine. The DOM-based nature of the vulnerability means that traditional server-side XSS protections may not prevent exploitation, as the malicious code is injected directly into the browser's DOM structure during page rendering. This makes detection and prevention more challenging for security teams who must monitor client-side behavior rather than server-side input validation.
The impact of CVE-2018-6076 aligns with CWE-79, which describes Cross-Site Scripting vulnerabilities in web applications, and specifically relates to CWE-116 for improper encoding or escaping of output. The vulnerability also maps to ATT&CK technique T1211, which covers the exploitation of weaknesses in web applications through DOM-based XSS attacks. Organizations should prioritize immediate patching of affected Chrome versions to prevent exploitation, as the vulnerability existed in versions prior to 65.0.3325.146. Additionally, implementing Content Security Policy headers, regular security testing, and user education about suspicious website visits can provide additional defense layers against similar attacks. The vulnerability underscores the importance of proper input validation and output encoding in browser security mechanisms, particularly for handling fragment identifiers and other URL components that can be manipulated by attackers to bypass security controls.