CVE-2023-28879: Artifex Ghostscript Buffer Overflow Flaw

CVE-2023-28879 Overview

CVE-2023-28879 is a buffer overflow vulnerability affecting Artifex Ghostscript through version 10.01.0. The flaw exists in the base/sbcp.c file and can lead to potential corruption of data internal to the PostScript interpreter. This vulnerability specifically affects the BCPEncode, BCPDecode, TBCPEncode, and TBCPDecode functions. The issue occurs when the write buffer is filled to one byte less than full, and an attempt is made to write an escaped character, resulting in two bytes being written instead of one.

Critical Impact

This buffer overflow vulnerability can be exploited remotely without authentication, potentially leading to arbitrary code execution, data corruption, or system compromise on affected systems running vulnerable versions of Ghostscript.

Affected Products

• Artifex Ghostscript through version 10.01.0
• Debian Linux 10.0
• Debian Linux 11.0

Discovery Timeline

• 2023-03-31 - CVE-2023-28879 published to NVD
• 2025-02-14 - Last updated in NVD database

Technical Details for CVE-2023-28879

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), a type of memory corruption flaw that occurs when a program writes data outside the boundaries of allocated memory. In the context of CVE-2023-28879, the issue manifests in Ghostscript's Binary Control Protocol (BCP) encoding and decoding functions.

The vulnerable code path is triggered during PostScript document processing when handling escaped characters in binary data streams. When the internal write buffer reaches a state where it has exactly one byte of remaining capacity, and the code attempts to write an escaped character sequence that requires two bytes, the buffer boundary is exceeded. This off-by-one error condition causes data to be written beyond the allocated buffer space.

The potential consequences of this vulnerability include corruption of adjacent memory structures within the PostScript interpreter, which could be leveraged by an attacker to achieve arbitrary code execution. Since Ghostscript is commonly used in document processing pipelines, print servers, and web applications for PDF/PostScript rendering, successful exploitation could have significant security implications across enterprise environments.

Root Cause

The root cause of this vulnerability is an improper boundary check in the base/sbcp.c source file. The code fails to account for the fact that escaped characters in the BCP protocol require two bytes of output space (the escape byte plus the actual character). When the buffer has only one byte remaining and an escaped character needs to be written, the code proceeds to write both bytes, overflowing the buffer by one byte.

This is a classic off-by-one buffer overflow condition where the boundary validation logic does not properly consider the variable-length nature of escaped character sequences in the binary encoding scheme.

Attack Vector

The attack vector for CVE-2023-28879 is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by crafting a malicious PostScript or PDF document that triggers the vulnerable code path when processed by Ghostscript.

Common attack scenarios include:

1. Document Processing Services: Uploading malicious documents to web applications that use Ghostscript for rendering or conversion
2. Print Server Exploitation: Sending crafted print jobs to servers using Ghostscript for processing
3. Email Gateway Attacks: Attaching malicious documents to emails processed by systems using Ghostscript for preview generation
4. Image Conversion Services: Exploiting applications that use Ghostscript to convert between document formats

The vulnerability can be triggered by carefully constructing input that causes the BCP encoder to fill the buffer to exactly one byte less than capacity, then forces an escaped character write operation.

Detection Methods for CVE-2023-28879

Indicators of Compromise

• Unexpected crashes or segmentation faults in Ghostscript processes (gs, gsc, or gswin64c)
• Abnormal memory consumption patterns in Ghostscript-related services
• Suspicious PostScript or PDF files with unusual BCP-encoded content in document processing queues
• Evidence of heap or stack corruption in crash dumps from Ghostscript processes

Detection Strategies

• Monitor for Ghostscript process crashes with signatures indicating buffer overflow conditions in memory analysis
• Implement file integrity monitoring on Ghostscript binaries and configuration files
• Deploy network-level inspection for malicious document uploads targeting document processing endpoints
• Use endpoint detection solutions to identify exploitation attempts through behavioral analysis of Ghostscript processes

Monitoring Recommendations

• Enable verbose logging for Ghostscript operations in production environments to capture processing anomalies
• Configure alerting on repeated Ghostscript process restarts or crashes that may indicate exploitation attempts
• Monitor network traffic to document processing services for unusual patterns or large volumes of document submissions
• Implement application-layer firewalls with document inspection capabilities to detect malformed PostScript/PDF content

How to Mitigate CVE-2023-28879

Immediate Actions Required

• Update Artifex Ghostscript to version 10.01.1 or later, which contains the fix for this vulnerability
• Apply vendor-provided security patches for affected Linux distributions (Debian, Fedora, Gentoo)
• Audit systems to identify all instances of Ghostscript installation and ensure they are updated
• Review and restrict network access to services that process documents using Ghostscript

Patch Information

Artifex has released a patch to address this vulnerability. The fix involves proper boundary checking before writing escaped characters to ensure the buffer has sufficient capacity for the full two-byte escaped sequence.

Relevant security advisories and patches:

• Ghostscript Bug Report #706494 - Official vendor bug report and fix details
• Debian Security Advisory DSA-5383 - Debian security update
• Debian LTS Announcement - Debian Long Term Support advisory
• Gentoo GLSA 202309-03 - Gentoo Linux security advisory
• Fedora package updates available through standard package management channels

Workarounds

• Disable or restrict Ghostscript processing of untrusted documents until patches can be applied
• Implement input validation to reject potentially malicious PostScript/PDF files before Ghostscript processing
• Run Ghostscript processes in sandboxed environments with restricted permissions to limit impact of potential exploitation
• Use the -dSAFER flag when invoking Ghostscript to enable restricted execution mode, though this may not fully prevent exploitation

# Example configuration for running Ghostscript with security restrictions
gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=output.pdf input.ps

# Verify Ghostscript version to ensure patched version is installed
gs --version
# Should return 10.01.1 or higher for patched versions