CVE-2017-9739 in Ghostscript GhostXPS
Summary
by MITRE
The Ins_JMPR function in base/ttinterp.c in Artifex Ghostscript GhostXPS 9.22 allows remote attackers to cause a denial of service (heap-based buffer over-read and application crash) or possibly have unspecified other impact via a crafted document.
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Analysis
by VulDB Data Team • 12/14/2022
The vulnerability identified as CVE-2017-9739 resides within the Ins_JMPR function located in the base/ttinterp.c file of Artifex Ghostscript GhostXPS version 9.22. This flaw represents a critical security issue that affects the interpretation of PostScript and PDF documents within the Ghostscript rendering engine. The vulnerability manifests as a heap-based buffer over-read condition that occurs during the processing of specially crafted documents, potentially leading to application instability and denial of service scenarios. The issue stems from insufficient bounds checking during the interpretation of jump instructions within the TrueType interpreter component of Ghostscript, which is responsible for rendering font data and executing font programs.
The technical implementation of this vulnerability involves the Ins_JMPR function failing to properly validate input parameters when processing jump operations within font programs. When a maliciously crafted document contains specially constructed TrueType font data, the interpreter attempts to execute a jump instruction that references memory locations beyond the allocated buffer boundaries. This over-read condition can result in the application accessing invalid memory addresses, leading to application crashes and potential information disclosure. The vulnerability is particularly concerning because it can be triggered through normal document processing without requiring user interaction, making it suitable for remote exploitation in web-based or document processing environments.
From an operational impact perspective, this vulnerability creates significant risks for organizations that rely on Ghostscript for document rendering and processing. The heap-based buffer over-read can cause unpredictable application behavior, including complete application crashes that disrupt document processing workflows. In environments where Ghostscript is used as a backend service for document conversion, print processing, or web-based document handling, such vulnerabilities can lead to service interruption and denial of service conditions. The potential for unspecified other impacts suggests that attackers might be able to leverage this vulnerability for more sophisticated attacks, including information disclosure or privilege escalation depending on the execution context.
The vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and represents a classic example of improper input validation in interpreter components. From an ATT&CK framework perspective, this vulnerability maps to the T1059.007 technique for executing malicious code through interpreter-based attacks, as well as T1499.004 for denial of service attacks targeting application stability. Organizations should consider implementing multiple mitigations including immediate patching of affected Ghostscript versions, network segmentation to limit exposure, and implementing document validation controls that can detect and block suspicious font data. Additionally, monitoring for application crashes and unusual memory access patterns can help identify exploitation attempts, while restricting document processing to trusted sources provides an additional layer of defense against remote exploitation attempts.
The remediation strategy should prioritize updating to Ghostscript versions that contain the patched Ins_JMPR function implementation, with particular attention to version 9.23 and later releases where the vulnerability has been addressed. System administrators should also consider implementing runtime protections such as address space layout randomization and stack canaries to mitigate potential exploitation. Regular security assessments of document processing workflows and font handling components should be conducted to identify similar vulnerabilities in other interpreter-based systems that may be susceptible to similar buffer over-read conditions.