CVE-2017-9740 in Ghostscript GhostXPS
Summary
by MITRE
The xps_decode_font_char_imp 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.
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Analysis
by VulDB Data Team • 12/14/2022
The vulnerability identified as CVE-2017-9740 resides within the GhostXPS component of Artifex Ghostscript version 9.22, specifically in the xps_decode_font_char_imp function located in xps/xpsfont.c. This flaw represents a heap-based buffer over-read condition that can be exploited by remote attackers through the careful crafting of XPS documents. The vulnerability manifests when the application processes malformed font data within XPS files, creating a scenario where memory access occurs beyond the bounds of allocated heap buffers. Such buffer over-read conditions typically arise when input validation is insufficient and the application fails to properly check array indices or buffer sizes before accessing memory locations. The security implications extend beyond simple denial of service as the vulnerability may potentially enable more severe consequences depending on the execution environment and memory layout.
The technical exploitation of this vulnerability leverages the improper handling of font character decoding within XPS document processing. When Ghostscript encounters a specially crafted XPS document containing malformed font data, the xps_decode_font_char_imp function attempts to read from heap memory locations that have not been properly validated or bounds-checked. This flaw falls under the category of CWE-125: "Out-of-bounds Read" which is a common vulnerability pattern in memory management operations where applications access memory beyond the intended buffer boundaries. The attack vector requires a remote user to submit a malicious XPS document to a system running GhostXPS 9.22, making this particularly concerning for web-based document processing services or applications that accept untrusted XPS files from external sources. The vulnerability's impact is categorized under the ATT&CK technique T1203: "Exploitation for Client Execution" as it enables remote code execution through document processing.
The operational impact of this vulnerability extends significantly beyond simple service disruption, as it can lead to complete application crashes and potential system instability. When exploited, the heap-based buffer over-read causes the Ghostscript application to access invalid memory locations, resulting in segmentation faults or access violations that terminate the process. This denial of service condition can be particularly problematic in environments where Ghostscript is used as a backend service for document conversion or printing operations, as it can effectively render the service unavailable to legitimate users. The potential for unspecified other impacts suggests that under certain conditions, this vulnerability might be exploitable for more advanced attacks including information disclosure or privilege escalation, though the primary documented risk remains denial of service. Organizations relying on Ghostscript for document processing should consider this vulnerability as a critical threat to system availability and service integrity.
Mitigation strategies for CVE-2017-9740 should prioritize immediate patching of affected Ghostscript installations to version 9.23 or later, which contains the necessary fixes for the buffer over-read condition. System administrators should implement strict input validation for all XPS documents processed through Ghostscript, including mandatory file format verification and content scanning before document rendering. Network-based mitigations can include implementing sandboxing or containerization of document processing services to limit the impact of potential exploitation, as well as deploying web application firewalls that can detect and block suspicious XPS document patterns. Organizations should also consider implementing automated monitoring for application crashes or unexpected terminations that could indicate exploitation attempts. The vulnerability demonstrates the importance of proper bounds checking in memory management operations and serves as a reminder of the critical need for thorough input validation in document processing systems. Additionally, security teams should maintain updated threat intelligence feeds to monitor for related vulnerabilities and exploitation patterns that may emerge in conjunction with this flaw.