CVE-2016-8602 in Ghostscript
Summary
by MITRE
The .sethalftone5 function in psi/zht2.c in Ghostscript before 9.21 allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted Postscript document that calls .sethalftone5 with an empty operand stack.
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Analysis
by VulDB Data Team • 11/29/2022
The vulnerability identified as CVE-2016-8602 represents a critical security flaw within the Ghostscript document processing library, specifically affecting versions prior to 9.21. This issue resides in the psi/zht2.c module and exploits the .sethalftone5 function to create conditions that can result in either application crash or potential arbitrary code execution. The vulnerability demonstrates the classic characteristics of a buffer overflow or stack manipulation flaw, where improper handling of input parameters leads to unpredictable system behavior. Ghostscript, widely used for rendering PostScript and PDF documents, serves as a foundational component in numerous document processing workflows across enterprise and consumer environments, making this vulnerability particularly concerning for security practitioners.
The technical exploitation of this vulnerability occurs through carefully crafted PostScript documents that manipulate the operand stack during execution of the .sethalftone5 function. When an attacker constructs a malicious document that calls this function with an empty operand stack, the underlying code fails to properly validate the stack state before proceeding with operations that assume certain values exist. This condition creates a scenario where the application attempts to access memory locations or execute operations that are not properly initialized, leading to segmentation faults or memory corruption. The vulnerability falls under CWE-129, which describes improper validation of array indices or buffer bounds, and also aligns with CWE-787, representing out-of-bounds write operations that can occur when stack manipulation is not properly controlled. The attack vector requires the victim to process a malicious PostScript document, making this a client-side exploitation scenario that can be delivered through email attachments, web downloads, or document sharing platforms.
The operational impact of CVE-2016-8602 extends beyond simple denial of service to potentially enable remote code execution, which represents a significant escalation in threat severity. When an application crashes due to this vulnerability, it creates opportunities for attackers to perform more sophisticated attacks such as privilege escalation or information disclosure. The potential for arbitrary code execution means that an attacker could gain control over the system running Ghostscript, which might be a print server, document conversion service, or any system that processes PostScript documents. This vulnerability particularly affects systems that automatically process or render PostScript content without proper sandboxing or input validation, including web applications that utilize Ghostscript for document conversion, enterprise print servers, and content management systems. The ATT&CK framework categorizes this vulnerability under T1059.007 for command and scripting interpreter, as the exploitation could lead to execution of malicious code through the compromised application, and potentially T1203 for exploitation for privilege escalation if the application runs with elevated permissions.
Mitigation strategies for CVE-2016-8602 primarily focus on immediate software updates and implementation of defensive measures to prevent exploitation. Organizations should prioritize upgrading to Ghostscript version 9.21 or later, which contains the necessary patches to address the operand stack validation issue. Additionally, implementing strict input validation for all PostScript documents processed by Ghostscript systems can provide defense-in-depth measures. Network segmentation and sandboxing techniques should be employed to limit the potential impact of successful exploitation attempts. Security monitoring should include detection of suspicious PostScript document processing activities, particularly those involving the .sethalftone5 function. Input sanitization and content filtering mechanisms should be deployed at network boundaries to prevent malicious documents from reaching systems that process PostScript content. System administrators should also implement least privilege principles for Ghostscript processes and consider implementing application whitelisting to prevent execution of untrusted PostScript documents. The vulnerability demonstrates the importance of proper stack management in interpreted languages and emphasizes the need for comprehensive testing of edge cases in document processing libraries.