CVE-2016-1643 in Chrome
Summary
by MITRE
The ImageInputType::ensurePrimaryContent function in WebKit/Source/core/html/forms/ImageInputType.cpp in Blink, as used in Google Chrome before 49.0.2623.87, does not properly maintain the user agent shadow DOM, which allows remote attackers to cause a denial of service or possibly have unspecified other impact via vectors that leverage "type confusion."
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Analysis
by VulDB Data Team • 07/10/2022
The vulnerability identified as CVE-2016-1643 resides within the WebKit rendering engine's implementation of HTML form elements, specifically targeting the ImageInputType::ensurePrimaryContent function in Blink. This flaw affects Google Chrome versions prior to 49.0.2623.87 and represents a critical security issue that exploits improper handling of the user agent shadow DOM structure. The vulnerability stems from the browser's failure to correctly maintain the shadow DOM boundaries when processing image input elements, creating a condition where attacker-controlled input can manipulate the internal DOM structure in unexpected ways.
The technical exploitation of this vulnerability involves type confusion attacks that leverage the improper maintenance of the user agent shadow DOM. When the ImageInputType::ensurePrimaryContent function processes image input elements, it fails to properly validate or sanitize the DOM structure, allowing malicious actors to inject or manipulate elements within the shadow DOM context. This type confusion occurs because the function does not adequately distinguish between different data types or object states, potentially causing the browser to interpret memory or object references incorrectly. The vulnerability is particularly dangerous because it operates within the browser's core rendering engine, where such flaws can cascade into more severe security implications beyond simple denial of service.
The operational impact of this vulnerability extends beyond simple denial of service, as the unspecified other impacts could include arbitrary code execution or privilege escalation within the browser sandbox. Attackers can potentially exploit this weakness to cause browser crashes, render pages unusable, or in more sophisticated scenarios, leverage the type confusion to execute malicious code within the browser's security boundaries. The shadow DOM manipulation capability provides attackers with a sophisticated vector for bypassing normal browser security mechanisms, as the user agent shadow DOM is typically protected from direct manipulation by web content. This vulnerability affects all users of affected Chrome versions and represents a significant risk to browser security.
Mitigation strategies for CVE-2016-1643 primarily involve immediate patching of affected Chrome installations to version 49.0.2623.87 or later, which contains the necessary fixes for the shadow DOM maintenance issues. Security administrators should also implement network-level protections such as content filtering and web application firewalls to detect and block exploitation attempts. Browser hardening measures including disabling unnecessary JavaScript features and implementing strict content security policies can reduce the attack surface. Organizations should conduct regular vulnerability assessments to identify potentially affected systems and ensure all browser components remain updated. This vulnerability aligns with CWE-457 and CWE-476 categories related to use of uninitialized variables and null pointer dereferences, and maps to ATT&CK techniques involving privilege escalation and code injection through browser exploitation. The fix implemented in the patched version addresses the core shadow DOM handling logic to prevent type confusion scenarios during image input element processing.