CVE-2026-110447: Collabora Online CODE Server RCE Vulnerability

CVE-2026-110447 Overview

CVE-2026-110447 is an OS command injection vulnerability in the Collabora Online Built-in CODE Server (richdocumentscode), a Nextcloud application. The flaw resides in proxy.php and triggers when the CODE server is not running, such as immediately after a product restart. Attackers can exploit the issue remotely without authentication to execute arbitrary operating system commands. The vulnerability affects versions before 26.4.303 and does not impact standalone Collabora Online servers. According to the CVE record, the flaw has been exploited in the wild during September and October 2026. This issue is distinct from CVE-2025-66208.

Critical Impact
Unauthenticated remote attackers can inject operating system commands via proxy.php, leading to full remote code execution on affected Nextcloud deployments.

Affected Products

Collabora Online Built-in CODE Server (richdocumentscode) before 26.4.303
Nextcloud instances running the Built-in CODE Server app
Deployments where the CODE server has been recently restarted or is not currently running

Discovery Timeline

2026-10-14 - CVE-2026-110447 published to NVD
2026-10-14 - Last updated in NVD database

Technical Details for CVE-2026-110447

Vulnerability Analysis

The vulnerability is classified as OS Command Injection [CWE-78]. It resides in the proxy.php component shipped with the richdocumentscode Nextcloud app. When the embedded CODE server process is not running, proxy.php enters a code path that passes attacker-controlled input to the underlying operating system shell without sufficient sanitization. Remote attackers can reach this endpoint over the network without authentication or user interaction. Successful exploitation yields command execution under the privileges of the Nextcloud web server process.

Root Cause

The root cause is improper neutralization of special elements used in an OS command. The proxy.php script constructs a command invocation that includes externally supplied data when the CODE server is unavailable. Because the input is not escaped or validated against a strict allowlist, shell metacharacters are interpreted by the operating system. The condition is reproducible when the application has recently restarted and the CODE backend has not yet become ready.

Attack Vector

The attack vector is network based. An unauthenticated attacker sends a crafted HTTP request to the proxy.php endpoint of a vulnerable Nextcloud instance. If the CODE server is not currently running, the injected command executes on the host. Because the CODE server state is observable through normal application behavior, attackers can time requests to coincide with service restarts. The CVE record states exploitation occurred in the wild in September and October 2026.

No verified public proof-of-concept code is available. For technical context, see the GitHub Issue Discussion and the Nextcloud User Update Request.

Detection Methods for CVE-2026-110447

Indicators of Compromise

HTTP requests targeting proxy.php within the richdocumentscode app path containing shell metacharacters such as ;, |, `, $(), or &&.
Unexpected child processes spawned by the Nextcloud PHP worker or web server user, particularly shells (sh, bash) and network utilities (curl, wget, nc).
Outbound connections from the Nextcloud host to unfamiliar infrastructure shortly after a CODE server restart.
New or modified files under the Nextcloud web root or temp directories without a matching administrative change.

Detection Strategies

Inspect web server access logs for requests to proxy.php that correlate with periods when the CODE server was not running.
Deploy endpoint behavioral monitoring to flag process lineage anomalies, where the web server parent spawns an interactive shell.
Alert on PHP interpreter processes invoking exec, system, popen, or shell binaries with argument strings containing URL-encoded metacharacters.

Monitoring Recommendations

Continuously monitor the health of the CODE server process so administrators are notified when it enters a restarted or stopped state.
Forward Nextcloud, PHP-FPM, and web server logs to a centralized logging platform for correlation with endpoint telemetry.
Baseline normal outbound network traffic from the Nextcloud host and alert on deviations such as reverse shells or data staging.

How to Mitigate CVE-2026-110447

Immediate Actions Required

Upgrade the richdocumentscode app to version 26.4.303 or later on all Nextcloud instances.
Audit web server, PHP, and system logs for evidence of exploitation dating back to September 2026.
Rotate credentials, API tokens, and secrets accessible to the Nextcloud host if compromise is suspected.
Isolate potentially compromised instances from the network until forensic review is complete.

Patch Information

Upgrade the Collabora Online Built-in CODE Server (richdocumentscode) Nextcloud app to version 26.4.303 or later. Standalone Collabora Online server deployments are not affected and do not require this update. Refer to the GitHub Issue Discussion and the Nextcloud User Update Request for vendor guidance.

Workarounds

Where immediate patching is not possible, migrate to a standalone Collabora Online server, which is not affected by this issue.
Restrict network access to the Nextcloud instance using a web application firewall or reverse proxy rules that block requests to proxy.php containing shell metacharacters.
Ensure the embedded CODE server process remains running at all times, since the vulnerable code path triggers when the service is down.

bash

# Configuration example: block suspicious proxy.php requests at the reverse proxy
# Nginx snippet for a Nextcloud frontend
location ~* /apps/richdocumentscode/proxy\.php$ {
    if ($args ~* "[;|\\x60\$\(\)&]") {
        return 403;
    }
    proxy_pass http://nextcloud_backend;
}