CVE-2011-3968 in iOS
Summary
by MITRE
Use-after-free vulnerability in Google Chrome before 17.0.963.46 allows remote attackers to cause a denial of service or possibly have unspecified other impact via vectors involving Cascading Style Sheets (CSS) token sequences.
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Analysis
by VulDB Data Team • 04/13/2021
The vulnerability identified as CVE-2011-3968 represents a critical use-after-free flaw in Google Chrome versions prior to 17.0.963.46 that specifically targets the browser's handling of Cascading Style Sheets token sequences. This type of vulnerability occurs when a program continues to reference memory that has already been freed, creating a dangerous condition that can be exploited by remote attackers to execute arbitrary code or cause system instability. The flaw manifests within Chrome's CSS parsing engine where improper memory management during token sequence processing leads to memory corruption. The vulnerability is particularly concerning because it can be triggered through web content without requiring user interaction, making it an ideal candidate for drive-by attack scenarios.
The technical implementation of this use-after-free vulnerability involves Chrome's CSS tokenization process where the browser parses stylesheet content and maintains references to memory structures containing parsed tokens. When processing certain malformed or complex CSS sequences, the parser fails to properly manage the lifecycle of allocated memory objects, leading to situations where freed memory blocks are accessed again. This memory management failure can be exploited by attackers who craft malicious CSS content designed to trigger the specific parsing path that leads to the use-after-free condition. The vulnerability's impact extends beyond simple denial of service to potentially allow remote code execution through carefully constructed attack vectors that leverage the memory corruption to inject and execute malicious code within the browser's memory space.
From an operational perspective, this vulnerability poses significant risks to users of older Chrome versions as it enables remote attackers to compromise systems through web-based attacks. The attack surface is broad since any web page containing malicious CSS content can trigger the vulnerability, making it particularly dangerous in environments where users visit untrusted websites or receive malicious emails with embedded web content. The potential impacts include complete system compromise, data theft, and persistent backdoor installation. Security researchers have classified this vulnerability as having a high severity rating due to its remote exploitability and the potential for arbitrary code execution. The vulnerability aligns with CWE-416 which specifically addresses use-after-free conditions, and represents a clear violation of secure coding practices that should prevent access to freed memory blocks.
Organizations and users must immediately update to Chrome version 17.0.963.46 or later to remediate this vulnerability. The patch addresses the memory management issues in the CSS parser by implementing proper reference counting and memory lifecycle management for token objects. Additional mitigations include implementing web application firewalls to filter malicious CSS content, enabling sandboxing features that limit the impact of potential exploitation, and deploying browser security extensions that provide additional protection layers. Network administrators should also consider implementing security controls that monitor for unusual CSS content patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of regular security updates and proper memory management practices in browser security architecture, as it highlights how seemingly benign parsing operations can lead to critical security flaws. This case study serves as a reminder of the complex security challenges inherent in modern web browsers and the need for continuous security auditing and vulnerability management processes.