CVE-2020-36773 – This vulnerability in Ghostscript allows attack... (How to Fix)

Q: What is the severity of CVE-2020-36773?

CVE-2020-36773 has a CVSS score of 9.8 (CRITICAL). This vulnerability in Ghostscript allows attackers to execute arbitrary code or cause denial of service by exploiting out-of-bounds write and use-after-free flaws in the txtwrite device. It affects systems processing PDF documents with Ghostscript before version 9.53.0. Organizations using Ghostscript for PDF processing, conversion, or rendering are at risk.

📋 TL;DR

This vulnerability in Ghostscript allows attackers to execute arbitrary code or cause denial of service by exploiting out-of-bounds write and use-after-free flaws in the txtwrite device. It affects systems processing PDF documents with Ghostscript before version 9.53.0. Organizations using Ghostscript for PDF processing, conversion, or rendering are at risk.

💻 Affected Systems

Products:

Artifex Ghostscript

Versions: All versions before 9.53.0

Operating Systems: All platforms running Ghostscript

Default Config Vulnerable: ⚠️ Yes

Notes: Affects any system using txtwrite device for PDF processing. Common in document conversion services, printing systems, and PDF rendering applications.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution leading to complete system compromise, data theft, or ransomware deployment.

🟠

Likely Case

Denial of service causing application crashes and service disruption during PDF processing.

🟢

If Mitigated

Limited impact with proper input validation and sandboxing, potentially only causing crashes.

🌐 Internet-Facing: HIGH - PDF processing services exposed to the internet can be directly targeted with malicious documents.

🏢 Internal Only: MEDIUM - Internal users could exploit via malicious PDFs, but requires user interaction or internal processing systems.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Proof-of-concept available in bug reports. Exploitation requires processing a specially crafted PDF document.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 9.53.0

Vendor Advisory: https://github.com/ArtifexSoftware/ghostpdl-downloads/releases/tag/gs9530

Restart Required: Yes

Instructions:

1. Download Ghostscript 9.53.0 or later from official sources. 2. Stop all Ghostscript services. 3. Install the updated version. 4. Restart services and verify functionality.

🔧 Temporary Workarounds

Disable txtwrite device

all

Prevent use of the vulnerable txtwrite device by removing or disabling it.

# Remove txtwrite device from Ghostscript installation
# Location varies by OS/distribution

Input validation and sandboxing

all

Implement strict input validation for PDF files and run Ghostscript in sandboxed/isolated environments.

🧯 If You Can't Patch

Implement network segmentation to isolate Ghostscript systems from critical assets
Deploy application allowlisting to prevent unauthorized code execution

🔍 How to Verify

Check if Vulnerable:

Check Ghostscript version with 'gs --version'. If version is below 9.53.0, system is vulnerable.

Check Version:

gs --version

Verify Fix Applied:

After patching, run 'gs --version' to confirm version 9.53.0 or higher is installed.

📡 Detection & Monitoring

Log Indicators:

Ghostscript crashes with segmentation faults
Unusual PDF processing errors
Memory access violation logs

Network Indicators:

Unusual PDF uploads to document processing services
Multiple failed PDF processing attempts

SIEM Query:

source="ghostscript" AND (event="segmentation fault" OR event="memory violation")

📊 Metadata

CVE ID: CVE-2020-36773

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-416

Published: February 4, 2024

Last Updated: May 22, 2025

🔗 References

https://bugs.ghostscript.com/show_bug.cgi?id=702229 Issue Tracking,Patch
https://bugzilla.opensuse.org/show_bug.cgi?id=1177922 Issue Tracking
https://git.ghostscript.com/?p=ghostpdl.git%3Ba=commit%3Bh=8c7bd787defa071c96289b7da9397f673fddb874 Broken Link
https://github.com/ArtifexSoftware/ghostpdl-downloads/releases/tag/gs9530 Release Notes
https://bugs.ghostscript.com/show_bug.cgi?id=702229 Issue Tracking,Patch
https://bugzilla.opensuse.org/show_bug.cgi?id=1177922 Issue Tracking
https://git.ghostscript.com/?p=ghostpdl.git%3Ba=commit%3Bh=8c7bd787defa071c96289b7da9397f673fddb874 Broken Link
https://github.com/ArtifexSoftware/ghostpdl-downloads/releases/tag/gs9530 Release Notes

📤 Share & Export

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📋 TL;DR

💻 Affected Systems

📦 What is this software?

Ghostscript by Artifex

Ghostscript by Artifex

Ghostscript by Artifex

Ghostscript by Artifex

Ghostscript by Artifex

⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Disable txtwrite device

Input validation and sandboxing

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

🔗 Related Vulnerabilities