CVE-2011-3437 in Mac OS X
Summary
by MITRE
Integer signedness error in Apple Type Services (ATS) in Apple Mac OS X 10.7 before 10.7.2 allows remote attackers to execute arbitrary code via a crafted embedded Type 1 font in a document.
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Analysis
by VulDB Data Team • 11/24/2021
The vulnerability identified as CVE-2011-3437 represents a critical integer signedness error within Apple Type Services, a core component of macOS operating systems. This flaw exists in Apple Mac OS X version 10.7 prior to 10.7.2, where the ATS framework fails to properly validate the signedness of integer values when processing Type 1 font data embedded within documents. The vulnerability stems from improper handling of signed and unsigned integer operations during font parsing, creating a condition where attacker-controlled data can manipulate memory operations. This issue falls under CWE-191, which specifically addresses integer underflow conditions, and can be categorized as a buffer overflow vulnerability through indirect manipulation of memory boundaries.
The technical exploitation of this vulnerability occurs when a malicious document containing a crafted Type 1 font is opened by a victim running an affected macOS version. Apple Type Services processes the embedded font data without proper bounds checking, allowing an attacker to manipulate integer values that control buffer allocation and memory access patterns. When the system attempts to parse the malformed font, the signedness error causes integer overflow or underflow conditions that result in improper memory allocation. This manipulation can lead to stack corruption or heap-based buffer overflows, enabling remote code execution with the privileges of the compromised user process. The attack vector is particularly dangerous as it requires no user interaction beyond opening the malicious document, making it a prime candidate for drive-by download attacks and social engineering campaigns.
The operational impact of CVE-2011-3437 extends beyond simple code execution to encompass complete system compromise potential. Attackers leveraging this vulnerability can execute arbitrary code remotely without requiring authentication or physical access to the target system. The exploitation chain typically involves crafting a malicious document with embedded Type 1 fonts that contain specially designed integer values to trigger the signedness error. Once successfully exploited, the vulnerability allows attackers to bypass standard security controls, potentially leading to full system compromise, data exfiltration, or establishment of persistent backdoors. This vulnerability affects all applications that utilize Apple Type Services for font rendering, including popular office suites, web browsers, and document viewers, making it particularly dangerous in enterprise environments where multiple applications may be vulnerable.
Mitigation strategies for CVE-2011-3437 primarily focus on immediate patch deployment and system hardening measures. Apple released security updates for Mac OS X 10.7.2 that address the integer signedness error in ATS by implementing proper bounds checking and signedness validation for integer operations. Organizations should prioritize immediate deployment of the applicable security patches to prevent exploitation. Additionally, implementing application whitelisting policies, disabling unnecessary font rendering capabilities, and monitoring for suspicious document opening activities can provide defense-in-depth measures. Network-level protections including web application firewalls and content filtering systems can help prevent delivery of malicious documents containing the vulnerable font structures. The vulnerability demonstrates the importance of proper integer handling in security-critical code components and aligns with ATT&CK technique T1059.007 for command and scripting interpreter execution, as successful exploitation typically results in code execution that can be leveraged for further attack progression within the compromised system environment.