CVE-2011-3443 in Safari
Summary
by MITRE
Use-after-free vulnerability in WebKit, as used in Apple Safari before 5.0.6, allows remote attackers to execute arbitrary code or cause a denial of service (heap memory corruption and application crash) via vectors related to improper list management for Cascading Style Sheets (CSS) @font-face rules.
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Analysis
by VulDB Data Team • 03/21/2021
The vulnerability identified as CVE-2011-3443 represents a critical use-after-free flaw within WebKit's CSS processing engine that affected Apple Safari versions prior to 5.0.6. This issue stems from improper memory management during the handling of Cascading Style Sheets @font-face rules, which are used to specify custom fonts for web page rendering. The vulnerability manifests when the web browser processes malformed or malicious CSS content that triggers incorrect memory deallocation patterns. According to CWE-416, this constitutes a classic use-after-free condition where memory is accessed after it has been freed, creating potential exploitation vectors for remote attackers. The flaw specifically impacts how WebKit manages memory allocation and deallocation for CSS objects during the rendering process, particularly when processing font-face declarations that reference external font resources.
The technical exploitation of this vulnerability occurs when a malicious web page presents specially crafted CSS code containing @font-face rules that manipulate the browser's internal list management structures. When Safari processes these rules, the WebKit engine improperly handles the memory cleanup of CSS objects, leading to a situation where freed memory locations are subsequently accessed or overwritten. This memory corruption can result in heap corruption that allows attackers to execute arbitrary code with the privileges of the browser process. The vulnerability is classified under the ATT&CK technique T1059.007 for command and script injection, as successful exploitation could enable attackers to run malicious code on affected systems. The improper list management aspect suggests that the vulnerability may involve double-free conditions or invalid pointer references within WebKit's CSS rendering subsystem, particularly affecting how the browser handles font resource loading and caching mechanisms.
The operational impact of CVE-2011-3443 extends beyond simple denial of service to encompass full remote code execution capabilities that could compromise user systems. When exploited, this vulnerability could allow attackers to gain persistent access to affected systems, potentially leading to data theft, system compromise, or further lateral movement within network environments. The heap memory corruption resulting from the use-after-free condition creates unpredictable behavior that attackers can leverage to overwrite critical memory structures, potentially redirecting program execution flow through return-oriented programming or other exploitation techniques. Users of affected Safari versions were particularly vulnerable as the flaw existed in the core rendering engine that processes all web content, making it difficult to defend against through traditional network-level security controls. The vulnerability demonstrates the critical importance of keeping browser software updated, as the issue was resolved through Apple's security updates that properly implemented memory management for CSS processing.
Mitigation strategies for CVE-2011-3443 require immediate patching of affected Safari installations to version 5.0.6 or later, which contains the necessary fixes for proper memory management in CSS @font-face rule processing. Organizations should implement browser security policies that enforce automatic updates and maintain current software versions across all user devices. Network administrators should consider implementing web filtering solutions that can block access to known malicious domains that might serve exploit code, though this approach provides only partial protection as the vulnerability exists within the browser's core functionality. The fix implemented by Apple likely involved strengthening memory management routines in WebKit's CSS parsing code, ensuring proper reference counting and object lifecycle management for CSS objects during font-face processing. Security teams should monitor for indicators of compromise related to this vulnerability through endpoint detection and response systems, looking for unusual memory access patterns or process behavior that might indicate exploitation attempts. Additionally, browser hardening measures such as sandboxing and memory protection features should be enabled to limit potential damage from successful exploitation attempts.