CVE-2016-1634 in Chrome
Summary
by MITRE
Use-after-free vulnerability in the StyleResolver::appendCSSStyleSheet function in WebKit/Source/core/css/resolver/StyleResolver.cpp in Blink, as used in Google Chrome before 49.0.2623.75, allows remote attackers to cause a denial of service or possibly have unspecified other impact via a crafted web site that triggers Cascading Style Sheets (CSS) style invalidation during a certain subtree-removal action.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability CVE-2016-1634 represents a critical use-after-free flaw within the Blink rendering engine that powers Google Chrome and other web browsers. This issue resides in the StyleResolver::appendCSSStyleSheet function located in WebKit/Source/core/css/resolver/StyleResolver.cpp, making it a core component of the browser's CSS processing pipeline. The vulnerability manifests when a malicious website triggers a specific sequence of events involving CSS style invalidation during subtree removal operations, creating a scenario where freed memory locations are accessed after they have been deallocated. This fundamental memory management error creates a dangerous condition that can be exploited by remote attackers to manipulate the browser's memory state.
The technical exploitation of this vulnerability occurs through a carefully crafted web page that leverages CSS properties to manipulate the document object model in ways that trigger the problematic code path. When the browser processes CSS stylesheets and encounters certain invalidation scenarios during subtree removal, the StyleResolver function fails to properly manage memory references, leading to a situation where pointers to deallocated memory are still being accessed. This use-after-free condition can result in unpredictable behavior including application crashes, memory corruption, or potentially more severe consequences depending on the memory layout and timing of the access. The vulnerability is particularly dangerous because it operates within the browser's core rendering engine, meaning that any web page loaded could potentially trigger this condition.
The operational impact of CVE-2016-1634 extends beyond simple denial of service scenarios to potentially enable more sophisticated attacks. While the primary effect is a denial of service through browser crashes, the use-after-free condition creates opportunities for memory corruption that could be leveraged for code execution under certain circumstances. Attackers could potentially craft malicious websites that force the browser into a state where controlled memory corruption occurs, potentially allowing for arbitrary code execution or privilege escalation. The vulnerability affects all versions of Google Chrome prior to 49.0.2623.75, making it particularly concerning given the widespread use of these older browser versions. The issue demonstrates how seemingly benign CSS processing operations can become attack vectors when memory management is not properly handled, highlighting the complexity of modern browser security architectures.
Mitigation strategies for CVE-2016-1634 primarily involve immediate browser updates to versions containing the patched code. Google released Chrome version 49.0.2623.75 which includes fixes addressing the memory management issues in the StyleResolver::appendCSSStyleSheet function. Organizations should prioritize updating their browser deployments and implement automated update mechanisms to ensure protection against this vulnerability. Additionally, network administrators can deploy web application firewalls and content filtering solutions that can detect and block known malicious patterns associated with this vulnerability. The fix implemented by Google addresses the root cause by ensuring proper memory management during CSS style invalidation operations and proper cleanup of references before memory deallocation. This vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software implementations. The attack pattern associated with CVE-2016-1634 would map to ATT&CK technique T1203, which covers exploitation of software vulnerabilities for privilege escalation and code execution. Organizations should also implement browser hardening measures including sandboxing, restricted permissions, and regular security audits to reduce the overall attack surface and mitigate potential exploitation of similar vulnerabilities in the browser rendering engine.