Collabora Online CODE Server RCE actively exploited (CVE-2026-110447)

Actively exploited in the wild - CVE-2026-110447 is a critical OS command injection in Collabora Online Built-in CODE Server before 26.4.303 (the richdocumentscode Nextcloud app) that grants unauthenticated remote code execution when the CODE server is not running. Update to 26.4.303 immediately.

Overview

The Built-in CODE Server app bundles the Collabora Online document engine directly into Nextcloud, so administrators can offer collaborative editing without a separate document server. CVE-2026-110447 lives in the app’s proxy.php script. When the CODE server process is not running - for example, right after a restart or during a crash - the proxy falls back to a code path that builds an operating system command from request input without adequate sanitization. An attacker can supply crafted input to inject additional shell commands, and those commands execute on the Nextcloud host.

The flaw is a different vulnerability than CVE-2025-66208, though both affect the same app. Standalone Collabora Online deployments are not affected. Only Nextcloud installations running the built-in CODE Server app are exposed.

CISA added this CVE to its Known Exploited Vulnerabilities catalog, and exploitation was observed in September and October 2026. The CVSS score is 9.2, with network attack vector, low complexity, no privileges required, and no user interaction. EPSS currently estimates a 1.2% chance of exploitation in the next 30 days, a figure that understates the risk given confirmed in-the-wild use.

Impact

Successful exploitation gives an unauthenticated attacker arbitrary command execution as the web server user on the Nextcloud host. That access can be used to read or modify the Nextcloud data directory, pivot to other internal services, install persistence, or stage further attacks. Because no credentials or user action are required, any internet-facing Nextcloud instance running a vulnerable copy of the app is a viable target. Documents, user data, and connected storage are all in reach.

Remediation and mitigation

• Update now. Upgrade the richdocumentscode app to 26.4.303 or later through the Nextcloud app store or your distribution’s package channel.
• Verify the running version on every Nextcloud instance, including those behind a reverse proxy, since an exposed proxy does not protect the app itself.
• Restrict access to the Nextcloud instance and its /apps/richdocumentscode paths at the network edge until patching is complete.
• Hunt for exploitation. Inspect web server and Nextcloud logs for unusual requests to proxy.php, especially around CODE server restarts, and review the host for unexpected processes or scheduled jobs.
• If compromise is suspected, rotate secrets, review outbound connections, and consult the Breach Reports at breach reports and the latest coverage in security news.

Security Insight

The fallback path that only triggers when a service is down is a classic blind spot: availability handling gets far less testing than steady-state operation, and attackers only need one restart window to hit it. CVE-2025-66208 already showed the richdocumentscode proxy is a worthwhile attack surface, and a second distinct command injection there suggests the app’s request handling needs a sustained audit rather than a one-off fix. Organizations that treat Nextcloud apps as third-party plugins with their own patch cadence, rather than as extensions of the core platform, are the ones most likely to remain exposed after this wave of exploitation.

Further Reading

• All Critical Vulnerabilities
• Recent Critical Vulnerabilities
• Top Critical CVEs