CVE-2024-29506: Artifex Ghostscript Buffer Overflow Flaw

CVE-2024-29506 Overview

CVE-2024-29506 is a stack-based buffer overflow vulnerability affecting Artifex Ghostscript versions before 10.03.0. The vulnerability exists in the pdfi_apply_filter() function, which fails to properly validate the length of PDF filter names before copying them to a stack-allocated buffer. When processing a maliciously crafted PDF document containing an excessively long filter name, the function can overflow the stack buffer, potentially enabling attackers to execute arbitrary code or crash the application.

Ghostscript is a widely deployed interpreter for PostScript and PDF files, commonly used in document conversion, printing systems, and preview applications. This vulnerability is particularly concerning because Ghostscript is often invoked automatically when processing untrusted PDF documents, making it an attractive target for exploitation through malicious file delivery.

Critical Impact

Attackers can exploit this stack-based buffer overflow through crafted PDF documents to potentially achieve remote code execution on systems running vulnerable Ghostscript versions, compromising confidentiality, integrity, and availability.

Affected Products

• Artifex Ghostscript versions prior to 10.03.0
• Applications and services that use Ghostscript for PDF/PostScript processing
• Document conversion pipelines and printing systems incorporating vulnerable Ghostscript installations

Discovery Timeline

• 2024-07-03 - CVE-2024-29506 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-29506

Vulnerability Analysis

The vulnerability is classified under CWE-787 (Out-of-bounds Write) and CWE-120 (Buffer Copy without Checking Size of Input). The pdfi_apply_filter() function in Ghostscript's PDF interpreter handles the application of various filters to PDF streams. When parsing filter names from a PDF document, the function copies the name into a stack-allocated buffer without adequately validating that the input length does not exceed the buffer's capacity.

This oversight allows an attacker to craft a PDF document with an abnormally long filter name that, when processed by Ghostscript, overwrites adjacent stack memory. Stack-based buffer overflows are particularly dangerous because they can overwrite return addresses and other control flow data, potentially allowing an attacker to redirect execution to shellcode or perform return-oriented programming (ROP) attacks.

The vulnerability requires user interaction in the form of opening or processing a malicious PDF file. However, in many deployment scenarios, Ghostscript processes documents automatically as part of document conversion workflows, email processing, or print spooling systems, which could facilitate exploitation without direct user action.

Root Cause

The root cause of this vulnerability is insufficient bounds checking in the pdfi_apply_filter() function when handling PDF filter names. The code copies filter name data into a fixed-size stack buffer without verifying that the source data length is within acceptable limits. This classic buffer overflow pattern occurs when trusted input assumptions are violated by maliciously crafted data.

The fix, as indicated in the Ghostscript Git Commit, implements proper length validation before the buffer copy operation, ensuring that oversized filter names are rejected or truncated safely.

Attack Vector

The attack is network-exploitable, as malicious PDF documents can be delivered through various channels including email attachments, web downloads, or document sharing platforms. The attack requires user interaction to open or process the crafted PDF file. Once the vulnerable pdfi_apply_filter() function processes the malicious filter name, the stack overflow occurs.

Successful exploitation could allow an attacker to:

• Execute arbitrary code with the privileges of the Ghostscript process
• Cause a denial of service by crashing the application
• Potentially escalate privileges if Ghostscript runs with elevated permissions

For detailed technical information about this vulnerability, refer to the Ghostscript Bug Report #707510 and the Openwall OSS-Security Discussion.

Detection Methods for CVE-2024-29506

Indicators of Compromise

• PDF files containing abnormally long filter names in stream dictionaries
• Ghostscript process crashes with stack corruption indicators
• Unexpected child process spawning from Ghostscript processes
• Memory access violations or segmentation faults in Ghostscript logs

Detection Strategies

• Implement file integrity monitoring for Ghostscript binaries and libraries
• Deploy endpoint detection and response (EDR) solutions that monitor for buffer overflow exploitation patterns
• Use application whitelisting to control which processes can be spawned by Ghostscript
• Monitor for anomalous PDF file characteristics such as excessively long string values in metadata or stream parameters

Monitoring Recommendations

• Enable crash dump collection for Ghostscript processes to facilitate post-incident analysis
• Configure security information and event management (SIEM) rules to alert on repeated Ghostscript failures
• Implement network traffic inspection to identify and quarantine suspicious PDF documents before processing
• Monitor system logs for exploitation indicators such as unexpected network connections from document processing services

How to Mitigate CVE-2024-29506

Immediate Actions Required

• Upgrade Artifex Ghostscript to version 10.03.0 or later immediately
• Audit systems for vulnerable Ghostscript installations, including embedded or bundled versions in third-party applications
• Implement network-level filtering to block or quarantine suspicious PDF documents
• Consider disabling automatic PDF processing in email and document handling systems until patching is complete
• Restrict Ghostscript execution privileges using sandboxing or containerization techniques

Patch Information

The vulnerability is addressed in Artifex Ghostscript version 10.03.0. Organizations should update to this version or later to remediate the vulnerability. The patch implements proper bounds checking in the pdfi_apply_filter() function to prevent stack buffer overflows when processing PDF filter names.

For detailed patch information, refer to the Ghostscript Git Commit containing the fix.

Workarounds

• Run Ghostscript in a sandboxed environment or container to limit the impact of potential exploitation
• Implement input validation at the application layer to reject PDF documents with suspicious characteristics before passing them to Ghostscript
• Use Ghostscript's -dSAFER flag to restrict file system and command execution capabilities
• Disable unnecessary PDF features and filters if your use case allows

# Run Ghostscript with restricted permissions
gs -dSAFER -dBATCH -dNOPAUSE -sDEVICE=pdfwrite -sOutputFile=output.pdf input.pdf

# Verify installed Ghostscript version
gs --version
# Ensure version is 10.03.0 or later