CVE-2018-16539 in Ghostscript
Summary
by MITRE
In Artifex Ghostscript before 9.24, attackers able to supply crafted PostScript files could use incorrect access checking in temp file handling to disclose contents of files on the system otherwise not readable.
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Analysis
by VulDB Data Team • 05/07/2023
CVE-2018-16539 represents a critical file disclosure vulnerability within the Ghostscript document processing library that affects versions prior to 9.24. This vulnerability stems from inadequate access control mechanisms during temporary file handling operations, specifically when processing crafted PostScript files. The flaw allows attackers to bypass normal file system permissions and access files that would typically be restricted or protected from unauthorized reading. The vulnerability is particularly concerning because it leverages the legitimate temporary file creation functionality within Ghostscript to execute unauthorized file access operations. Attackers can craft malicious PostScript documents that, when processed by an affected Ghostscript version, trigger the flawed temporary file handling logic and subsequently read arbitrary files from the system. This issue falls under the CWE-22 category of Improper Limitation of a Pathname to a Restricted Directory, commonly known as Path Traversal, and aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter. The vulnerability is classified as a privilege escalation issue since it allows low-privilege users to access files they should not normally be able to read, effectively circumventing the operating system's file permission controls. The technical implementation involves Ghostscript's temporary file creation process where the application generates temporary files in system directories without proper validation of the file paths or access permissions. When processing malicious PostScript input, the application fails to properly validate that the temporary file operations remain within designated boundaries, allowing attackers to manipulate the temporary file handling logic to access restricted system files. This type of vulnerability is particularly dangerous in environments where Ghostscript is used for document processing, such as web applications, print servers, or document management systems, as it can lead to unauthorized disclosure of sensitive information. The impact extends beyond simple file reading, as attackers could potentially access configuration files, user data, or system files that contain authentication credentials or other sensitive information. Organizations using Ghostscript in production environments should prioritize immediate patching to version 9.24 or later, as the vulnerability can be exploited remotely through web-based document processing systems. The fix implemented in version 9.24 addresses the core issue by strengthening access controls during temporary file operations and implementing proper validation of file paths to prevent unauthorized access to system resources. Security teams should also consider implementing additional monitoring and access controls around Ghostscript processes, particularly in multi-tenant environments where document processing occurs, to detect potential exploitation attempts. The vulnerability demonstrates the importance of proper input validation and access control mechanisms in document processing libraries, as these tools often run with elevated privileges to handle complex document formats and are frequently targeted by attackers seeking to exploit their capabilities for information disclosure.