CVE-2023-36664: Artifex Ghostscript Privilege Escalation

CVE-2023-36664 Overview

CVE-2023-36664 is a command injection vulnerability in Artifex Ghostscript through version 10.01.2 that stems from improper permission validation for pipe devices. The vulnerability occurs when Ghostscript processes files containing the %pipe% prefix or the | pipe character prefix, allowing attackers to execute arbitrary commands on the target system. This flaw enables malicious actors to craft specially designed PostScript or PDF files that, when processed by Ghostscript, can execute arbitrary system commands with the privileges of the user running the application.

Critical Impact

Successful exploitation allows attackers to achieve arbitrary command execution through maliciously crafted documents processed by Ghostscript, potentially leading to complete system compromise.

Affected Products

• Artifex Ghostscript versions through 10.01.2
• Debian Linux 11.0 and 12.0
• Fedora 37 and 38

Discovery Timeline

• 2023-06-25 - CVE-2023-36664 published to NVD
• 2024-12-05 - Last updated in NVD database

Technical Details for CVE-2023-36664

Vulnerability Analysis

This command injection vulnerability exists because Ghostscript fails to properly validate permissions when handling pipe devices. Ghostscript supports special device syntax that allows output to be piped to external commands. The %pipe% prefix and the | pipe character are used to redirect output through system commands, but the permission validation mechanism does not adequately restrict this functionality.

When a user opens or processes a malicious PostScript or PDF file, Ghostscript interprets embedded directives that leverage pipe device syntax. Without proper permission checks, these directives can execute arbitrary shell commands on the underlying operating system. This is particularly dangerous because Ghostscript is commonly used by many applications and services for document conversion, printing subsystems, and image processing pipelines.

The vulnerability is classified under CWE-552 (Files or Directories Accessible to External Parties), indicating that the core issue relates to improper access control over system resources that should be restricted.

Root Cause

The root cause lies in Ghostscript's inadequate permission validation when processing pipe device specifications. The interpreter fails to properly sanitize or restrict the use of pipe-based output devices, allowing embedded commands within document files to be executed directly by the operating system shell. This represents a failure in the input validation and access control mechanisms that should prevent untrusted document content from invoking system-level operations.

Attack Vector

The attack requires local access where a user must interact with a maliciously crafted file—typically by opening a PostScript (.ps) or PDF document containing the exploit payload. Attack scenarios include:

1. A victim downloads and opens a malicious PDF file received via email or downloaded from the internet
2. An application that uses Ghostscript for document processing automatically renders a malicious file
3. Print spoolers or document management systems that leverage Ghostscript process an uploaded malicious document

The malicious document contains specially crafted PostScript commands that abuse the pipe device functionality to execute arbitrary system commands. When Ghostscript processes the file, it interprets these commands and passes them to the underlying shell for execution.

For technical details on the vulnerability mechanism, refer to the Ghostscript Bug Report which documents the specific issue with pipe device handling.

Detection Methods for CVE-2023-36664

Indicators of Compromise

• Unusual process spawning from Ghostscript (gs) processes, particularly shell commands or network utilities
• PostScript or PDF files containing %pipe% strings or suspicious pipe character sequences
• Unexpected outbound network connections originating from document processing applications
• System logs showing command execution that correlates with document processing events

Detection Strategies

• Monitor process creation events for child processes spawned by gs, ghostscript, or related binaries
• Implement file content inspection for documents containing %pipe% or | followed by command strings
• Deploy behavioral analysis to detect anomalous command execution patterns from document rendering processes
• Review application logs from services using Ghostscript for processing errors or unusual activity

Monitoring Recommendations

• Configure endpoint detection and response (EDR) solutions to alert on suspicious process chains involving Ghostscript
• Implement file integrity monitoring for Ghostscript binaries and configuration files
• Enable detailed audit logging for processes executing document conversion operations
• Monitor for PostScript interpreter warnings or errors that may indicate exploitation attempts

How to Mitigate CVE-2023-36664

Immediate Actions Required

• Upgrade Artifex Ghostscript to version 10.01.3 or later immediately
• Apply distribution-specific patches from Debian, Fedora, or Gentoo as appropriate for your environment
• Restrict Ghostscript execution to trusted documents only until patching is complete
• Consider temporarily disabling Ghostscript functionality in applications where it is not critical

Patch Information

Artifex has released patches addressing this vulnerability in Ghostscript versions after 10.01.2. The fixes are available through the following commits:

• Ghostscript Commit 0974e4f
• Ghostscript Commit 505eab7

Distribution-specific advisories and patches are available:

• Debian Security Advisory DSA-5446
• Gentoo GLSA 202309-03
• Fedora package updates available via the Fedora Package Announcement

Workarounds

• Use the -dSAFER flag when invoking Ghostscript to restrict file system access and disable potentially dangerous features
• Implement application sandboxing or containerization for services that process untrusted documents with Ghostscript
• Deploy network segmentation to limit the impact of potential command execution from document processing systems
• Configure file upload validation to scan incoming documents for suspicious content before Ghostscript processing

# Example: Running Ghostscript with SAFER mode enabled
gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=output.pdf input.ps

# Verify installed Ghostscript version
gs --version

# Update Ghostscript on Debian/Ubuntu
sudo apt update && sudo apt install --only-upgrade ghostscript

# Update Ghostscript on Fedora
sudo dnf update ghostscript