CVE-2025-46646: Artifex Ghostscript UTF-8 Vulnerability

CVE-2025-46646 Overview

CVE-2025-46646 is an input validation vulnerability affecting Artifex Ghostscript versions prior to 10.05.0. The flaw exists in the decode_utf8 function within base/gp_utf8.c, where overlong UTF-8 encoding sequences are mishandled. This vulnerability represents an incomplete fix for a previously identified issue (CVE-2024-46954), indicating that the original remediation did not fully address the underlying security concern.

Critical Impact

Improper handling of overlong UTF-8 encoding can lead to security bypass scenarios where malicious input evades validation checks, potentially enabling path traversal or other input-based attacks against systems processing PostScript or PDF files through Ghostscript.

Affected Products

• Artifex Ghostscript versions prior to 10.05.0

Discovery Timeline

• 2025-04-26 - CVE-2025-46646 published to NVD
• 2025-06-23 - Last updated in NVD database

Technical Details for CVE-2025-46646

Vulnerability Analysis

The vulnerability resides in Ghostscript's UTF-8 decoding implementation. UTF-8 encoding allows characters to be represented using variable-length byte sequences (1-4 bytes). The specification mandates that each character must be encoded using the shortest possible sequence. However, "overlong" encodings use more bytes than necessary to represent a character, which can be exploited to bypass security filters that check for specific character patterns.

When the decode_utf8 function in base/gp_utf8.c processes input, it fails to properly reject overlong UTF-8 sequences. This incomplete validation allows attackers to craft malicious input that appears benign to security checks but decodes to dangerous values. The vulnerability is classified under CWE-24 (Path Traversal: '../filedir'), suggesting potential exploitation for directory traversal attacks.

This issue exists because the previous fix for CVE-2024-46954 did not comprehensively address all overlong encoding edge cases, leaving a residual attack surface.

Root Cause

The root cause is incomplete input validation in the UTF-8 decoding logic. The decode_utf8 function does not adequately verify that multi-byte UTF-8 sequences use the minimal number of bytes required for each character. This allows overlong representations (e.g., encoding ASCII characters using 2, 3, or 4 bytes instead of 1) to pass through validation checks.

Attack Vector

The attack vector is local, requiring an attacker to have the ability to supply malicious input to a Ghostscript process. This could occur through:

• Processing a specially crafted PostScript or PDF document
• Supplying malicious filenames or path parameters
• Exploiting applications that use Ghostscript as a backend for document processing

Attackers can leverage overlong UTF-8 sequences to represent path traversal characters (such as ../) in a way that bypasses initial validation but resolves to the intended malicious path during processing.

The vulnerability mechanism involves crafting UTF-8 sequences that evade pattern-based security filters. For detailed technical information about the specific encoding issues, refer to the Ghostscript Bug Report #708311 and the official commit f14ea81e that addresses this issue.

Detection Methods for CVE-2025-46646

Indicators of Compromise

• Unexpected file access attempts outside of intended directories during Ghostscript document processing
• Anomalous UTF-8 byte sequences in input files processed by Ghostscript, particularly multi-byte representations of ASCII characters
• Log entries indicating path resolution to unexpected locations during PDF or PostScript rendering

Detection Strategies

• Monitor Ghostscript process activity for attempts to access files outside designated working directories
• Implement file integrity monitoring on systems running Ghostscript to detect unauthorized file access
• Deploy endpoint detection rules that identify suspicious input patterns containing overlong UTF-8 sequences

Monitoring Recommendations

• Enable verbose logging for Ghostscript operations to capture file access patterns
• Monitor for process behavior anomalies when Ghostscript handles external or untrusted documents
• Implement network monitoring for systems that process documents from external sources

How to Mitigate CVE-2025-46646

Immediate Actions Required

• Upgrade Artifex Ghostscript to version 10.05.0 or later immediately
• Restrict Ghostscript processing to trusted documents only until patching is complete
• Review and audit any custom integrations or scripts that invoke Ghostscript with external input

Patch Information

Artifex has addressed this vulnerability in Ghostscript version 10.05.0. The fix is available in commit f14ea81e6c3d2f51593f23cdf13c4679a18f1a3f. Organizations should update to the patched version through their package manager or by downloading directly from the Artifex website.

Workarounds

• Implement input sanitization at the application layer before passing data to Ghostscript
• Use Ghostscript's -dSAFER option to restrict file system access capabilities
• Consider sandboxing Ghostscript processes using containerization or OS-level isolation mechanisms

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