CVE-2016-2844 in Chrome
Summary
by MITRE
WebKit/Source/core/layout/LayoutBlock.cpp in Blink, as used in Google Chrome before 49.0.2623.75, does not properly determine when anonymous block wrappers may exist, which allows remote attackers to cause a denial of service (incorrect cast and assertion failure) or possibly have unspecified other impact via crafted JavaScript code.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability identified as CVE-2016-2844 resides within the WebKit rendering engine's Blink component, specifically in the LayoutBlock.cpp file that handles layout calculations for web content. This flaw affects Google Chrome versions prior to 49.0.2623.75 and represents a critical issue in the browser's document object model handling. The vulnerability stems from improper detection mechanisms that fail to accurately identify when anonymous block wrappers should be created during the layout process, creating a scenario where malicious JavaScript code can exploit this gap in logic.
The technical implementation of this vulnerability involves the browser's layout engine incorrectly managing the creation and handling of anonymous block wrappers in CSS layout calculations. When the rendering engine processes certain JavaScript constructs that manipulate the DOM structure, it fails to properly account for the existence of anonymous block wrappers that should be automatically generated by the CSS specification. This incorrect logic leads to situations where the engine attempts to cast objects to inappropriate types or triggers assertion failures during layout calculations, ultimately resulting in browser instability.
From an operational perspective, this vulnerability presents significant risks to users of affected Chrome versions. Attackers can craft malicious JavaScript code that specifically targets this layout engine flaw, potentially causing denial of service conditions where the browser crashes or becomes unresponsive. The impact extends beyond simple service disruption as the vulnerability may also enable more sophisticated attacks that could lead to arbitrary code execution or information disclosure, depending on how the underlying assertion failures are exploited. The vulnerability is particularly dangerous because it can be triggered through standard web browsing activities, making it difficult to prevent through user behavior alone.
The flaw aligns with CWE-119, which addresses "Improper Access to Memory Location" and specifically relates to memory corruption issues that arise from incorrect handling of object types during runtime operations. Additionally, this vulnerability maps to ATT&CK technique T1059.007 for "Command and Scripting Interpreter: JavaScript" as it leverages JavaScript code execution to exploit the underlying rendering engine flaw. The vulnerability demonstrates a classic case of improper input validation where the layout engine fails to properly validate the structure of CSS and DOM elements during processing.
Mitigation strategies for this vulnerability require immediate patching of affected Chrome versions to 49.0.2623.75 or later, which contains the necessary fixes for the layout engine's anonymous block wrapper detection logic. Organizations should also implement network-level protections such as content filtering and web application firewalls to prevent exploitation attempts, though these measures are not foolproof. Browser hardening techniques including sandboxing and privilege separation should be maintained to limit the potential impact if exploitation occurs. Regular security updates and patch management processes are essential to prevent similar vulnerabilities from being exploited in the future, particularly given the complex nature of modern web rendering engines that must handle thousands of different CSS and DOM combinations.