Source: cve@mitre.org
The ghostscript command with the -dSAFER option allows remote attackers to execute commands.
Ghostscript, a popular PostScript interpreter, is vulnerable to remote command execution when the -dSAFER option is used incorrectly. This allows attackers to bypass the intended security restrictions and execute arbitrary code on the server, potentially leading to complete system compromise and data exfiltration.
Step 1: Payload Preparation: The attacker crafts a malicious PostScript file containing commands designed to exploit the Ghostscript vulnerability. This file may include commands to execute shell commands or access restricted files.
Step 2: Payload Delivery: The attacker delivers the malicious PostScript file to the target system. This could be done through various means, such as uploading the file to a web server, sending it via email, or exploiting another vulnerability that allows file upload.
Step 3: Ghostscript Execution: The attacker triggers the execution of Ghostscript with the malicious PostScript file, typically using the -dSAFER option to attempt to bypass security restrictions. The command might look like: gs -dSAFER -q -sDEVICE=pdfwrite -sOutputFile=/tmp/output.pdf malicious.ps
Step 4: Vulnerability Exploitation: Ghostscript, despite the -dSAFER option, processes the malicious PostScript code. The crafted PostScript code exploits the vulnerability to execute arbitrary commands on the server. This could involve creating files, deleting files, or executing shell commands.
Step 5: Command Execution: The attacker's commands are executed on the target system, potentially leading to data exfiltration, system compromise, or further exploitation.
The vulnerability stems from flaws in how Ghostscript's -dSAFER option is implemented. While intended to restrict file access and prevent malicious PostScript code execution, the implementation contains weaknesses that allow attackers to bypass these restrictions. Specifically, the interpreter's handling of certain PostScript operators or constructs, even with -dSAFER enabled, can be manipulated to execute shell commands. This is often achieved through crafted PostScript code that leverages vulnerabilities in the interpreter's internal functions or its interaction with the operating system. The root cause is a failure to comprehensively sanitize or restrict all potential attack vectors within the PostScript language, allowing for the creation of malicious PostScript files that can execute arbitrary commands. This is not a single specific buffer overflow or race condition, but rather a collection of weaknesses in the overall security model of the interpreter.
While no specific APTs are exclusively known for exploiting this specific CVE, it is a common attack vector used by various threat actors to gain initial access or escalate privileges. This vulnerability is often used in conjunction with other vulnerabilities. This vulnerability is not listed on the CISA KEV.
Monitor for suspicious Ghostscript command-line arguments, especially those involving -dSAFER, -sOutputFile, and potentially unusual file paths or extensions (e.g., .ps, .eps).
Analyze Ghostscript process activity for unexpected network connections or file system modifications.
Examine Ghostscript logs for error messages or suspicious activity related to PostScript file processing.
Implement file integrity monitoring to detect unauthorized modifications to critical system files.
Network Intrusion Detection Systems (IDS) can be configured to detect malicious PostScript code patterns.
Upgrade Ghostscript to the latest version to address known vulnerabilities.
Carefully review and restrict the use of Ghostscript, especially in environments where untrusted PostScript files are processed.
If possible, avoid using Ghostscript with the -dSAFER option, as it may not provide sufficient protection. Consider alternative document processing tools.
Implement input validation and sanitization to prevent the execution of malicious PostScript code.
Restrict the permissions of the user account running Ghostscript to the minimum necessary.
Regularly audit Ghostscript configurations and security settings.
Implement a Web Application Firewall (WAF) to filter malicious requests that may attempt to exploit this vulnerability.