Ghostscript flaw lets hackers hijack servers via PDF uploads
A critical heap buffer overflow vulnerability (CVE-2026-39919) in the Ghostscript interpreter and rendering engine could allow remote code execution through specially crafted PDF files.
A critical heap buffer overflow vulnerability (CVE-2026-39919) in the Ghostscript interpreter and rendering engine could allow remote code execution through specially crafted PDF files.
The flaw was discovered on August 23 by researchers at Defiant’s platform Wordfence using their Argus AI-powered system.
Ghostscript is a PostScript and PDF interpreter that can render PDFs as images, generate thumbnails for previews, and optimize PDF files by compressing embedded images and removing unnecessary font data.
When generating a PDF thumbnail, WordPress can use the PHP Imagick extension to call ImageMagick, which launches Ghostscript.
A specially crafted PDF file containing a JPEG 2000 image can trigger incorrect handling of low-bit-depth samples and mismatched component resolutions.
Using Argus, the researchers developed two exploits for CVE-2026-39919 that force Ghostscript to write 1,024 bytes into a 256-byte buffer, corrupting nearby memory and leading to unauthenticated remote code execution in a WordPress deployment.
Wordfence focused on WordPress systems, but notes that the flaw affects any online system running Ghostscript 9.21 through 10.07.1 and is exploitable if the payload is adjusted to the environment.
The researchers tested ten Linux environments, including Debian, Ubuntu, Fedora, Alpine, and AlmaLinux, as well as an official WordPress Docker image snapshot, and found that all contained the vulnerable code.
Tested environments
Source: Wordfence
The researchers tested two proof-of-concept (PoC) exploits and found that their ability to trigger the vulnerability depended on the target environment.
In a lab testbed, they executed the exploits 10,240 times against Linux packages but failed to achieve remote code execution. However, they successfully executed code remotely on a purpose-built test server.
The researchers found that modifying the PDF’s fonts, language settings, font configuration, and one core system library enabled the exploit to succeed, although not reliably.
In WordPress environments specifically, successful exploitation has four prerequisites:
- An attacker can upload a PDF, anonymously or through a low-privileged account.
- The site processes that PDF to generate a preview or thumbnail.
- The processing chain reaches Ghostscript, with the necessary software and policy settings permitting PDF rendering.
- Ghostscript contains the unpatched vulnerable decoding code.
Wordfence noted that stock WordPress does not permit anonymous Media Library uploads.
More generally, any application that renders attacker-supplied PDFs through affected Ghostscript code may expose the flaw, and authentication requirements for exploitation depend on the application.
Artifex, the maintainer of Ghostscript, rolled out a fix on September 8, in version 10.08.0 of the interpreter.
Fixes were also backported to older versions, so users should check the revision details for patch status.
WordPress administrators need to ensure, through their hosting provider, that Ghostscript has been upgraded to version 10.08.0 or later.
If using Docker, it is recommended to rebuild and redeploy with an updated, patched base image.
If unable to upgrade to a fixed Ghostscript release, it is recommended to block PDF uploads to the server or disable PDF rendering in ImageMagick.
Wordfence said it has not seen any in-the-wild exploitation of CVE-2026-39919 yet.
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