CVE-2020-36773 is a critical security vulnerability affecting Artifex Ghostscript versions prior to 9.53.0. The flaw exists in the txtwrite device implementation within the file devices/vector/gdevtxtw.c. Specifically, the vulnerability arises due to improper handling of character codes in PDF documents where a single character code can correspond to multiple Unicode code points, such as ligatures. This leads to an out-of-bounds write and use-after-free conditions. These memory corruption issues can be exploited by an attacker who crafts a malicious PDF file containing such character codes. When Ghostscript processes this PDF, the vulnerability can be triggered, potentially allowing arbitrary code execution, complete compromise of the host system, or denial of service. The CVSS v3.1 base score is 9.8, indicating a critical severity with network attack vector, no required privileges or user interaction, and high impact on confidentiality, integrity, and availability. Although no public exploits are currently known in the wild, the nature of the vulnerability and the critical score suggest a high risk if exploited. Ghostscript is widely used for processing PostScript and PDF files in many environments, including document rendering, printing services, and PDF conversion tools. The vulnerability affects all versions before 9.53.0, so any deployment using older versions is at risk. The underlying issues correspond to CWE-787 (Out-of-bounds Write) and CWE-416 (Use After Free), both serious memory safety errors that can lead to arbitrary code execution or system crashes.

For European organizations, the impact of this vulnerability can be significant. Many enterprises, government agencies, and service providers rely on Ghostscript for document processing workflows, including automated PDF rendering, printing, and conversion services. Exploitation could allow attackers to execute arbitrary code on critical servers, leading to data breaches, disruption of document services, or lateral movement within networks. Confidentiality could be compromised by exfiltration of sensitive documents or credentials. Integrity could be undermined by tampering with document contents or system configurations. Availability could be affected by crashes or denial of service conditions. Sectors such as finance, healthcare, public administration, and legal services, which handle large volumes of PDF documents, are particularly at risk. Additionally, since the vulnerability requires no authentication or user interaction and can be triggered remotely by processing a malicious PDF, it poses a high risk in environments where untrusted PDFs are ingested automatically or by users. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as proof-of-concept exploits may emerge.

European organizations should immediately audit their use of Ghostscript and identify any instances running versions prior to 9.53.0. The primary mitigation is to upgrade Ghostscript to version 9.53.0 or later, where this vulnerability has been fixed. If upgrading is not immediately possible, organizations should implement strict input validation and filtering to block or quarantine untrusted PDF files, especially those from external or unknown sources. Sandboxing Ghostscript processes to limit the impact of potential exploitation is recommended, using containerization or operating system-level restrictions. Monitoring logs for unusual Ghostscript activity or crashes can provide early detection of exploitation attempts. Network segmentation should be applied to isolate systems that process PDFs from critical infrastructure. Additionally, organizations should educate users about the risks of opening untrusted PDFs and implement email gateway protections to detect and block malicious attachments. Regular vulnerability scanning and patch management processes should be enforced to ensure timely updates.