U.S. Cybersecurity and Infrastructure Security Agency (CISA) adds Collabora Online flaw to its Known Exploited Vulnerabilities catalog.
The U.S. Cybersecurity and Infrastructure Security Agency (CISA) added a Collabora Collabora Online – Built-in CODE Server flaw, tracked as CVE-2026-110447 (CVSS score of 9.2), to its Known Exploited Vulnerabilities (KEV) catalog.
Collabora Online – Built-in CODE Server is an app for Nextcloud that lets you open, edit and collaborate on documents, spreadsheets and presentations directly in your browser, without needing Microsoft Office installed on your computer. It is based on Collabora Online and LibreOffice technology.
CVE-2026-110447 is a critical OS command injection flaw in Nextcloud’s proxy.php that affects Collabora Online Built-in CODE Server before 26.4.303. Unauthenticated attackers can execute commands when the built-in server is stopped. Standalone Collabora servers are not affected. Update immediately.
In versions up to 26.4.302, proxy.php included request data in a Bash command without proper sanitization, allowing attackers to execute OS commands as the web server user. Exploitation is possible only when the local CODE server is stopped, such as during a restart, upgrade or crash. The script runs directly through the web server without loading Nextcloud’s code.
Exploitation has been reported since September 2026, with attackers deploying PHP web shells and stealing configuration files containing credentials and application secrets.
Three administrators reported the vulnerability on GitHub, while the first recorded attack dates back to September 10. The first attack was reported by a Nextcloud administrator whose servers had been compromised. Logs showed malicious requests on September 10 and 11, 2026, from the same IP, targeting proxy.php on version 26.4.302. The attackers deployed a PHP web shell and searched one server for credential stores and cryptocurrency wallets. Although reviewed logs showed no file exfiltration commands, data accessible to the web server account must be considered potentially exposed.
Two other administrators reported similar incidents, but none found evidence of root access. After updating to 26.4.303, one administrator recorded another attempt on September 14, but no new shell appeared. Project maintainer mmeeks urged users to update and remove leftover shx*.php files. The CVE record confirms exploitation in September and October 2026, but the total number of compromised servers remains unknown. The flaw affects only the Development Edition’s Built-in CODE Server deployment.
According to Binding Operational Directive (BOD) 22-01: Reducing the Significant Risk of Known Exploited Vulnerabilities, FCEB agencies have to address the identified vulnerabilities by the due date to protect their networks against attacks exploiting the flaws in the catalog.
Experts also recommend that private organizations review the Catalog and address the vulnerabilities in their infrastructure.
CISA orders federal agencies to fix the flaw by October 26, 2026.
Follow me on Twitter: @securityaffairs and Facebook and Mastodon
(SecurityAffairs – hacking, CISA)
