Nextcloud Collabora Vulnerability: CVE-2026-110447

A critical flaw in the Collabora document editor that ships inside Nextcloud, CVE-2026-110447, is being actively exploited, and Nextcloud admins have already found webshells planted on affected servers. If you run Nextcloud with the built-in Collabora CODE Server for editing Office documents, the job today is a version check and, if you need it, a one-app update. This note is for whoever manages that Nextcloud install, in-house or at an MSP, and it stays narrow on purpose: this bug affects one specific app configuration, not Nextcloud itself.

The warning first went out on the Nextcloud community forum on October 3, 2026, where users reported finding webshells on their servers before anyone had a CVE number to put on it. The formal record, CVE-2026-110447, followed on October 14, 2026, scored 9.2 out of 10. As of this writing, none of the major security outlets have covered it yet, so acting now puts you ahead of the news cycle rather than behind it.

What CVE-2026-110447 actually lets an attacker do

In plain English: the app that lets Nextcloud start its own built-in copy of Collabora can be tricked into running commands it was never supposed to run.

The built-in CODE Server app, called richdocumentscode, starts Collabora by calling out to the operating system with PHP’s exec() function. A file called proxy.php is supposed to hand that process clean, safe input. It does not neutralize that input carefully enough, and there is a specific window where the gap opens wide: right after the CODE server has stopped or restarted, before it comes back up. During that window, a crafted request to proxy.php can inject operating-system commands instead of the data it expects. That is CWE-78, OS command injection, and it does not require a login first.

This is a different bug from CVE-2025-66208, an older, lower-severity issue in the same app that depended on a misconfigured reverse proxy. Do not assume a fix you applied for that one covers this.

Are you exposed

Start here, because the honest answer calms most readers down: running Nextcloud, or even running Collabora inside it for document editing, is not the problem. Giving staff a way to edit Word and Excel files in the browser is normal, useful infrastructure. The question is narrower than “do we use Nextcloud.”

Your setup	Affected by CVE-2026-110447
Collabora Online - Built-in CODE Server (richdocumentscode) app, version 26.4.302 or earlier	Yes
Collabora Online - Built-in CODE Server, version 26.4.303 or later	No, already patched
Standalone Collabora Online server	No
Collabora via Docker or a Linux distribution package	No
Commercial Collabora hosting	No
richdocuments without the built-in CODE Server app	No

The built-in app exists so smaller Nextcloud installs do not have to stand up and maintain a separate Collabora server just to edit documents. That convenience is exactly what carries the risk here: the app starts its editing engine with a shell command instead of a safer integration, and only this specific delivery method does that.

What to do today

A short, specific list.

1. Check which app you actually run. In Nextcloud, go to the Apps page and look for “Collabora Online - Built-in CODE Server.” If it is not installed, or if you run Collabora standalone, via Docker, or through a commercial host, this CVE does not apply to you.
2. Check the version. If richdocumentscode is installed, confirm the version is 26.4.303 or later.
3. Update if you are behind. Update through the Nextcloud apps page, or run occ app:update richdocumentscode from the command line.
4. Look for signs you were already hit. Check for PHP files you do not recognize in your Nextcloud data and app directories, unexpected processes running as the web server user, and unusual outbound connections from the host. Nextcloud admins are actively finding webshells right now, so this step is worth the few minutes it takes.
5. If you find a webshell, do not just delete it. Take the server offline, treat it as a compromise, and restore from a known-good backup or rebuild, then patch before bringing it back online. A single deleted file does not undo whatever an attacker did while they had a shell.

Most readers who check step one will find they do not run the affected app at all, and that is the whole task.

The bigger lesson for self-hosted collaboration tools

Nextcloud exists because a business wants its own files, its own server, and its own control, instead of handing everything to a SaaS vendor. That is a reasonable trade. It also means the vendor is not the one watching for advisories and pushing an automatic update. Someone on your side has to be.

That someone does not need to be watching constantly. A periodic, independent look at what your business actually runs and whether it is current is the point of an external penetration test, and if Nextcloud sits inside your network rather than facing the internet directly, an internal penetration test covers that angle too. Between tests, some teams keep a continuous watch running. Our own service for that, Blindsight, watches the code and dependencies a business ships itself. It does not watch a self-hosted platform like Nextcloud, so today’s job is still the richdocumentscode update in front of you, not a tool problem.

The pattern behind today’s advisory is not exotic. A convenience feature, turned on for a good reason, ran a command it should not have trusted. Knowing exactly which apps and versions are running on your systems, before someone else checks for you, is most of the job either way.

Not sure what’s running on your Nextcloud server, or anywhere else on your network? Tell us a little about your setup and what’s prompting the question, and we’ll come back with a fair, fixed quote. Request a quote.