CVE-2018-16509 in Ghostscript
Summary
by MITRE
An issue was discovered in Artifex Ghostscript before 9.24. Incorrect "restoration of privilege" checking during handling of /invalidaccess exceptions could be used by attackers able to supply crafted PostScript to execute code using the "pipe" instruction.
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Analysis
by VulDB Data Team • 12/02/2024
The vulnerability identified as CVE-2018-16509 represents a critical privilege escalation flaw within the Artifex Ghostscript PDF rendering engine, affecting versions prior to 9.24. This issue stems from inadequate validation mechanisms during exception handling, specifically when processing /invalidaccess exceptions within the PostScript interpreter. The flaw allows malicious actors to exploit the software's privilege restoration logic, creating a pathway for arbitrary code execution through carefully crafted PostScript payloads.
The technical root cause of this vulnerability lies in the improper handling of privilege levels during exception processing. When Ghostscript encounters an invalid access condition, it should properly restrict privileges to prevent unauthorized operations. However, the implementation contains a logic flaw where privilege restoration occurs incorrectly, allowing attackers to maintain elevated privileges even after encountering access violations. This misconfiguration enables the exploitation of the pipe instruction, which serves as a mechanism for executing external commands through the PostScript interpreter, effectively bypassing normal security boundaries.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with a means to perform privilege escalation attacks within systems running vulnerable Ghostscript versions. The pipe instruction, when improperly controlled, can be leveraged to execute arbitrary system commands, potentially leading to complete system compromise. This vulnerability affects any system that processes PostScript or PDF documents through Ghostscript, including web applications, document management systems, and print servers that rely on the software for rendering capabilities. The attack vector requires only the ability to submit crafted PostScript content, making it particularly dangerous in environments where users can upload or process untrusted document formats.
The vulnerability aligns with CWE-284, which addresses improper access control, and demonstrates characteristics consistent with privilege escalation attacks in interpreter-based systems. From an ATT&CK framework perspective, this flaw maps to techniques involving privilege escalation and command execution through legitimate system tools, specifically leveraging the interpreter's native capabilities to bypass security controls. The exploitation process typically involves crafting PostScript code that triggers an invalid access condition, then using the flawed privilege restoration mechanism to maintain elevated privileges long enough to execute malicious pipe operations.
Mitigation strategies for CVE-2018-16509 primarily focus on immediate software updates to Ghostscript version 9.24 or later, which contain the necessary fixes to address the privilege restoration logic. Organizations should also implement strict input validation and sanitization for all PostScript and PDF content processed through Ghostscript, particularly in web-facing applications. Additional protective measures include running Ghostscript with reduced privileges, implementing network segmentation to limit access to vulnerable systems, and monitoring for suspicious command execution patterns. Security administrators should also consider implementing sandboxing mechanisms and content filtering to prevent the execution of potentially malicious PostScript constructs, ensuring that any document processing occurs within isolated environments that limit the impact of successful exploits.