CVE-2011-3966 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 related to error handling for Cascading Style Sheets (CSS) token-sequence data.
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Analysis
by VulDB Data Team • 04/13/2021
The vulnerability identified as CVE-2011-3966 represents a critical use-after-free flaw in Google Chrome versions prior to 17.0.963.46 that specifically targets the browser's CSS token-sequence error handling mechanisms. This type of vulnerability falls under the CWE-416 category, which defines use-after-free conditions as a fundamental memory safety issue where program code continues to reference memory after it has been freed, potentially leading to unpredictable behavior and security consequences. The flaw manifests during the processing of malformed CSS content, particularly when Chrome encounters invalid token sequences that trigger error handling routines.
The technical exploitation of this vulnerability occurs when Chrome's rendering engine processes malformed CSS data that contains invalid token sequences, causing the browser to allocate memory for CSS parsing structures and subsequently free them during error handling. However, the error handling code fails to properly manage the reference counts or memory states, allowing an attacker to manipulate the freed memory through carefully crafted CSS content. This manipulation can occur through various CSS properties and selectors that trigger the vulnerable code path, particularly those involving complex parsing scenarios or malformed declarations that cause the browser to enter error handling modes.
The operational impact of this vulnerability extends beyond simple denial of service, as the use-after-free condition creates potential for more severe consequences including arbitrary code execution. When the freed memory is accessed after being reallocated, attackers can potentially inject malicious code into the browser process, leveraging the memory corruption to escalate privileges or bypass security controls. The vulnerability's remote exploitability means that attackers can deliver malicious CSS content through web pages, making it particularly dangerous in the context of web browsing where users expect to encounter diverse and potentially untrusted content. This aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as the vulnerability could enable attackers to execute arbitrary code within the browser context, potentially leading to full system compromise.
Mitigation strategies for CVE-2011-3966 primarily focus on immediate browser updates to versions 17.0.963.46 and later, which contain the necessary patches to address the memory management issues in CSS error handling. Organizations should implement comprehensive patch management processes to ensure all Chrome installations are updated promptly, as this vulnerability was actively exploited in the wild. Additional protective measures include implementing content security policies that restrict external CSS loading, using web application firewalls to filter malicious CSS content, and deploying browser hardening configurations that limit the browser's attack surface. Security monitoring should include detection of unusual memory access patterns and error handling behaviors that might indicate exploitation attempts. The vulnerability highlights the importance of robust memory management in browser engines and demonstrates how seemingly minor error handling flaws can create significant security risks, particularly when combined with the complex parsing requirements of modern web technologies.