CVE-2020-16307 in Ghostscript
Summary
by MITRE
A null pointer dereference vulnerability in devices/vector/gdevtxtw.c and psi/zbfont.c of Artifex Software GhostScript v9.50 allows a remote attacker to cause a denial of service via a crafted postscript file. This is fixed in v9.51.
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Analysis
by VulDB Data Team • 08/13/2020
The null pointer dereference vulnerability identified as CVE-2020-16307 represents a critical security flaw within the GhostScript document processing system developed by Artifex Software. This vulnerability exists in two key components of the software architecture: devices/vector/gdevtxtw.c and psi/zbfont.c, which handle text rendering and font processing operations respectively. The flaw manifests when the system processes specially crafted PostScript files that contain malformed font data or text formatting instructions. When GhostScript attempts to render these malicious inputs, the software encounters a scenario where a pointer variable intended to reference font data becomes null, yet the application proceeds to dereference this null pointer without proper validation, resulting in an immediate system crash or termination.
The technical exploitation of this vulnerability occurs through remote code execution pathways that leverage the PostScript language's capabilities for embedding and processing font information. Attackers can craft malicious PostScript documents that contain invalid font references or malformed font table structures, specifically targeting the text writing device implementation in gdevtxtw.c and the font processing logic in zbfont.c. The underlying cause aligns with CWE-476, which describes null pointer dereference conditions in software implementations. This particular flaw demonstrates how font processing components in document rendering systems can become attack vectors when proper input validation and pointer safety checks are absent. The vulnerability operates at the intersection of software robustness and security, where insufficient error handling in text rendering components creates a pathway for denial of service attacks that can be initiated remotely without requiring authentication or elevated privileges.
The operational impact of CVE-2020-16307 extends beyond simple system crashes, as it can be leveraged for broader denial of service scenarios that affect document processing services, print servers, and web applications that utilize GhostScript for rendering PDF or PostScript content. Organizations relying on GhostScript for automated document processing, content management systems, or web-based printing services face significant risk when exposed to this vulnerability, as attackers can systematically disrupt services by submitting malicious documents. The vulnerability particularly affects environments where GhostScript is used as a backend processing component for document conversion or rendering, including enterprise document management systems, online printing services, and content delivery platforms that process user-uploaded documents. The remote nature of the attack means that threat actors can exploit this vulnerability from any location without physical access to the target system, making it particularly dangerous for publicly accessible services.
Mitigation strategies for CVE-2020-16307 primarily involve immediate software updates to version 9.51 or later, which includes patches addressing the null pointer dereference conditions in both affected source files. Security administrators should implement comprehensive patch management protocols to ensure all instances of GhostScript within their infrastructure are updated promptly. Additionally, organizations should consider implementing input validation measures that filter or sanitize PostScript content before processing, particularly for systems that accept user-submitted documents. Network segmentation and access controls can help limit exposure by restricting access to GhostScript processing services to trusted internal networks only. The vulnerability's classification under ATT&CK technique T1059.007 for PostScript execution highlights the importance of monitoring and controlling the execution of scripting languages within document processing environments. Regular security assessments and vulnerability scanning should include checks for outdated GhostScript installations, as this vulnerability demonstrates how seemingly minor implementation flaws in core rendering components can create significant security risks for document processing systems.