CVE-2008-4236 in Mac OS X
Summary
by MITRE
Apple Type Services (ATS) in Apple Mac OS X 10.5 before 10.5.6 allows remote attackers to cause a denial of service (infinite loop) via a crafted embedded font in a PDF file.
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Analysis
by VulDB Data Team • 08/22/2019
Apple Type Services represents a critical component within Mac OS X responsible for handling font rendering and typography operations across the operating system. This subsystem processes font data from various sources including embedded fonts within PDF documents, making it a prime target for exploitation. The vulnerability exists in the font parsing logic where ATS fails to properly validate font structure parameters, particularly in handling malformed or maliciously crafted font data embedded within PDF files. When a user opens a specially crafted PDF containing an embedded font with malformed structure elements, the ATS processing engine enters an infinite loop during font parsing operations, causing the application to become unresponsive and ultimately resulting in a denial of service condition that affects the entire system.
The technical flaw manifests through improper bounds checking and validation mechanisms within the ATS font processing pipeline. When encountering embedded fonts with malformed header structures, invalid table offsets, or corrupted font metrics data, the parsing routines fail to implement adequate termination conditions or error recovery procedures. This lack of proper input validation creates a condition where the font processing loop continues indefinitely, consuming system resources and preventing normal application operation. The vulnerability specifically affects versions prior to 10.5.6 where Apple had not yet implemented sufficient defensive measures against malformed font data processing. The infinite loop occurs at the core level of font handling, making it particularly difficult to detect and mitigate through standard application-level protections.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be exploited remotely through malicious PDF documents delivered via email attachments, web downloads, or compromised websites. Attackers can craft PDF files with embedded fonts containing carefully constructed malformed data that triggers the infinite loop when the document is opened or even when the PDF is simply viewed in a preview mode. This makes the vulnerability particularly dangerous in enterprise environments where users may inadvertently open malicious documents, leading to system-wide service disruption. The vulnerability affects not only individual user applications but can also impact system stability and availability, particularly when multiple users are affected simultaneously through shared network resources or email systems.
Mitigation strategies for this vulnerability require immediate patch application to upgrade to Mac OS X 10.5.6 or later versions where Apple has implemented proper font validation and bounds checking mechanisms. System administrators should also implement proactive measures such as PDF document filtering and sandboxing of PDF viewing applications to limit the potential impact of malicious documents. The vulnerability aligns with CWE-129, which addresses improper validation of input ranges, and relates to ATT&CK technique T1203, representing the exploitation of software vulnerabilities for denial of service attacks. Additional protective measures include implementing network-based intrusion detection systems that can identify and block PDF files with suspicious embedded font structures, as well as educating users about the risks of opening untrusted PDF documents from unknown sources. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates across all affected systems.