CVE-2017-9620 in Ghostscript GhostXPS
Summary
by MITRE
The xps_select_font_encoding function in xps/xpsfont.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, related to the xps_encode_font_char_imp function.
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Analysis
by VulDB Data Team • 12/14/2022
The vulnerability identified as CVE-2017-9620 resides within the GhostXPS component of Artifex Ghostscript version 9.22, specifically in the xps_select_font_encoding function located in xps/xpsfont.c. This flaw represents a heap-based buffer over-read condition that can be triggered through maliciously crafted XPS documents, demonstrating a critical weakness in the document processing pipeline. The vulnerability stems from inadequate input validation and memory management within the font encoding selection mechanism, creating a scenario where untrusted data can overwrite adjacent memory regions.
The technical execution of this vulnerability occurs when the xps_encode_font_char_imp function processes font character data without proper bounds checking. This function receives input from the xps_select_font_encoding function, which fails to validate the font encoding parameters against the actual buffer boundaries. The heap-based buffer over-read manifests when the application attempts to read beyond the allocated memory space for font character encoding data, potentially accessing uninitialized memory or memory belonging to other processes. This memory corruption can result in immediate application crashes or more subtle issues that may allow for further exploitation.
From an operational impact perspective, this vulnerability creates significant risks for organizations relying on Ghostscript for document processing, particularly in environments where untrusted documents are processed. The denial of service aspect can disrupt critical printing operations, document conversion workflows, and automated processing systems that depend on Ghostscript functionality. Additionally, the unspecified other impacts referenced in the CVE description suggest potential for more severe consequences including information disclosure or privilege escalation, though these remain unproven. The vulnerability affects the core XPS document processing capabilities and can be exploited remotely through document upload mechanisms or email attachments.
Organizations should implement immediate mitigations including updating to Ghostscript version 9.23 or later, which contains the necessary patches to address the buffer over-read condition. Network segmentation and document validation controls should be deployed to prevent untrusted documents from reaching systems running Ghostscript. Input validation should be strengthened at multiple levels, including implementing strict bounds checking in font processing functions and employing memory safety techniques such as stack canaries or address sanitization. The vulnerability aligns with CWE-125: Buffer Under-read, which is categorized under the broader class of memory safety issues in the Common Weakness Enumeration catalog. From an attacker's perspective, this vulnerability maps to techniques in the ATT&CK framework under T1059.007: Command and Scripting Interpreter: PowerShell, as it could enable an attacker to execute malicious code through compromised document processing systems. System administrators should also consider implementing application whitelisting policies to restrict execution of vulnerable Ghostscript components and deploy intrusion detection systems to monitor for exploitation attempts. The patching process must be carefully managed to ensure that all instances of Ghostscript within the organization's infrastructure are updated, as the vulnerability can be exploited through various document processing pathways including web applications, email systems, and automated workflow systems.