CVE-2023-4042 - The Ghostscript Patch That Never Was—A Deep Dive Into Persistent Vulnerability
Ghostscript is famous for rendering PostScript and PDF files, running in everything from printers to Linux servers. It’s also famous (or infamous!) for its history of vulnerabilities—no surprise, given the complexity of its codebase. In the world of security patches, the difference between “fixed” and “not fixed” is huge—especially when systems are assumed secure based on public advisories.
What Happened?
A high-severity flaw, CVE-202-16305, was discovered in Ghostscript in 202, allowing potential command execution and other mischief via specially crafted files. Red Hat claimed to include the fix in RHSA-2021:1852-06, their security advisory. However, it turns out the fix was not shipped in their ghostscript package for Red Hat Enterprise Linux (RHEL) 8, even though documentation said otherwise. This led to a new identifier: CVE-2023-4042.
This vulnerability specifically affects RHEL 8’s Ghostscript. If you’re running another platform or Ghostscript version, you might be safe—double check just in case!
Why Is This a Big Deal?
Security-conscious admins trust vendor advisories. When the *actual* code doesn’t match the claimed patch level, users get left with a false sense of safety. That’s a critical liability—especially if Ghostscript is exposed to untrusted files (think: print servers, web apps, document processors).
The Original Flaw (CVE-202-16305)
This bug involves incorrect sanitization of filenames inside Ghostscript’s handling of certain file operations, allowing an attacker to escape to sensitive system files.
A simplified exploit example (not safe to use in real environments!)
% Ghostscript PostScript snippet exploiting CVE-202-16305
(file|/etc/passwd) (r) file run
If unpatched, this could let an attacker access system files they shouldn’t. If Ghostscript is part of a web service, it becomes an easy pathway for exfiltrating sensitive information.
The Missing Patch
Red Hat’s security bulletins, specifically RHSA-2021:1852-06, listed CVE-202-16305 as *fixed*. However, investigation showed the corresponding upstream patch was not included in the shipped package for RHEL 8. That means the vulnerability was accidentally left open.
How to Check for the Patch
Check if your system’s Ghostscript contains the fix by searching for the relevant code change. For example:
rpm -q ghostscript
# Check package version against RHEL’s fixed advisory
Or, inspect this code snippet in *gsio.c*
/* Vulnerable code: no filename sanitization */
fopen(filename, "r");
The patched version includes stricter file path validation.
Crafting an Exploit
If you’re an attacker or pentester (again, for *authorized* and educational use!), a malicious PostScript file could invoke system-level file access. For example:
(%pipe%id) (r) file run
This would run the id command on Unix. If Ghostscript is running under a privileged account or in a sensitive context, the consequences could be severe.
How to Fix This
If you’re on RHEL 8:
- Upgrade Ghostscript to a version *after* the true patch inclusion. Look for updated advisories—Red Hat will likely list a follow-up with CVE-2023-4042.
References and Links
- Red Hat RHSA-2021:1852-06
- Red Hat’s CVE-2023-4042 page
- Upstream Ghostscript fix for CVE-202-16305
- NVD entry for CVE-202-16305
The Takeaway
CVE-2023-4042 is a perfect example of why “trust but verify” is critical in security—sometimes even trusted vendor advisories don’t match reality. If you’re running Ghostscript on RHEL 8, double check your package version and apply any upcoming fixes. And remember: never run Ghostscript as root, and always validate untrusted files before processing.
Stay patched. Stay alert. Don’t let your trust in advisories be your weakest link.
Timeline
Published on: 08/23/2023 13:15:00 UTC
Last modified on: 08/29/2023 15:40:00 UTC