CVE-2020-16303
📋 TL;DR
A use-after-free vulnerability in GhostScript's XPS image processing allows remote attackers to execute arbitrary code via a malicious PDF file. This affects GhostScript v9.50 and earlier versions when processing untrusted documents. Systems using GhostScript for PDF rendering or conversion are vulnerable.
💻 Affected Systems
- Artifex Software GhostScript
- Applications that embed GhostScript (like ImageMagick, GIMP)
- PDF processing services
📦 What is this software?
Ghostscript by Artifex
Ubuntu Linux by Canonical
Ubuntu Linux by Canonical
Ubuntu Linux by Canonical
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the GhostScript process, potentially leading to full system compromise if GhostScript runs with elevated privileges.
Likely Case
Arbitrary code execution in the context of the GhostScript process, which could lead to data theft, lateral movement, or persistence establishment.
If Mitigated
Limited impact if GhostScript runs in a sandboxed environment with minimal privileges and no network access.
🎯 Exploit Status
The vulnerability requires crafting a malicious PDF file. Public exploit details are available in the bug tracker and commit diff.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v9.51
Vendor Advisory: https://bugs.ghostscript.com/show_bug.cgi?id=701818
Restart Required: Yes
Instructions:
1. Download GhostScript v9.51 or later from https://www.ghostscript.com. 2. Stop all GhostScript services. 3. Install the new version following platform-specific instructions. 4. Restart services.
🔧 Temporary Workarounds
Disable XPS device
allRemove or disable the XPS device to prevent exploitation via the vulnerable function
Remove xps device from GhostScript installation or configuration
Run GhostScript in sandbox
linuxRun GhostScript with minimal privileges and in a containerized environment
docker run --read-only --cap-drop=ALL ghostscript
chroot or seccomp-bpf for Linux systems
🧯 If You Can't Patch
- Implement strict input validation to reject suspicious PDF files before GhostScript processing
- Isolate GhostScript processes in network-restricted environments with no outgoing connections
🔍 How to Verify
Check if Vulnerable:
Check GhostScript version: gs --version. If output is 9.50 or lower, system is vulnerable.Check Version:
gs --versionVerify Fix Applied:
After patching, run gs --version and confirm version is 9.51 or higher. Test with known malicious PDF samples if available.📡 Detection & Monitoring
Log Indicators:
- GhostScript crash logs with segmentation faults in gdevxps.c
- Unusual process spawning from GhostScript
Network Indicators:
- Unexpected outbound connections from GhostScript processes
SIEM Query:
process_name:"gs" AND (event_type:"crash" OR parent_process:"gs")🔗 References
- https://bugs.ghostscript.com/show_bug.cgi?id=701818
- https://git.ghostscript.com/?p=ghostpdl.git%3Ba=commitdiff%3Bh=94d8955cb77
- https://lists.debian.org/debian-lts-announce/2020/08/msg00032.html
- https://security.gentoo.org/glsa/202008-20
- https://usn.ubuntu.com/4469-1/
- https://www.debian.org/security/2020/dsa-4748
- https://bugs.ghostscript.com/show_bug.cgi?id=701818
- https://git.ghostscript.com/?p=ghostpdl.git%3Ba=commitdiff%3Bh=94d8955cb77
- https://lists.debian.org/debian-lts-announce/2020/08/msg00032.html
- https://security.gentoo.org/glsa/202008-20
- https://usn.ubuntu.com/4469-1/
- https://www.debian.org/security/2020/dsa-4748
