CVE-2020-16293 in Ghostscript
Summary
by MITRE
A null pointer dereference vulnerability in compose_group_nonknockout_nonblend_isolated_allmask_common() in base/gxblend.c of Artifex Software GhostScript v9.50 allows a remote attacker to cause a denial of service via a crafted PDF file. This is fixed in v9.51.
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Analysis
by VulDB Data Team • 02/02/2026
The vulnerability CVE-2020-16293 represents a critical null pointer dereference flaw within the GhostScript PDF processing engine developed by Artifex Software. This issue exists in the compose_group_nonknockout_nonblend_isolated_allmask_common() function located in the base/gxblend.c source file, which is part of the graphics blending operations that GhostScript employs when rendering PDF documents. The vulnerability specifically affects GhostScript version 9.50 and earlier, with the issue being resolved in version 9.51. The flaw manifests when processing specially crafted PDF files that contain malformed graphics group operations, particularly those involving non-knockout, non-blend, isolated, and all-mask graphics compositions.
The technical nature of this vulnerability stems from insufficient input validation within the graphics blending pipeline of GhostScript's rendering engine. When a PDF file containing maliciously constructed graphics group data is processed, the function attempts to dereference a pointer that remains uninitialized or set to NULL, leading to an immediate program crash. This occurs because the code path assumes certain graphical elements will be properly initialized before being accessed, but malicious input can bypass these initialization checks. The vulnerability falls under CWE-476 which specifically addresses null pointer dereference conditions, making it a classic example of improper null pointer handling in security-critical software components. The issue demonstrates how graphics processing libraries can become attack vectors when they fail to properly validate complex data structures passed through PDF documents.
From an operational perspective, this vulnerability creates significant denial of service risks for systems that process untrusted PDF content, including email servers, document repositories, and web applications that accept PDF uploads. Remote attackers can exploit this weakness by crafting malicious PDF files that trigger the null pointer dereference during rendering operations, causing the GhostScript process to terminate unexpectedly. This type of attack can be particularly dangerous in automated environments where PDF processing occurs without human intervention, as it can lead to service disruption across entire systems. The ATT&CK framework categorizes this as a denial of service attack through software exploitation, specifically under the technique of process injection and application crash. Organizations relying on GhostScript for PDF rendering and processing face potential operational disruption when this vulnerability is exploited, as it can be triggered silently during normal document processing without requiring user interaction.
Mitigation strategies for CVE-2020-16293 primarily involve immediate deployment of the patched GhostScript version 9.51, which addresses the null pointer dereference by implementing proper input validation and pointer initialization checks. System administrators should prioritize updating their GhostScript installations across all environments where PDF processing occurs, particularly in web applications, document management systems, and automated processing pipelines. Additional protective measures include implementing PDF content filtering and sanitization layers that can detect and block suspicious graphics operations before they reach the GhostScript engine. Organizations should also consider deploying network-based intrusion detection systems that can identify patterns associated with malicious PDF files targeting this vulnerability. The fix implemented in version 9.51 demonstrates proper defensive programming practices by ensuring all pointers are validated before dereferencing and by implementing robust error handling for malformed graphics data, which aligns with security best practices outlined in the OWASP Top Ten and other industry security frameworks.