CVE-2026-28289: FreeScout 1.8.206 Patch Bypass for CVE-2026-27636 via Zero-Width Space Character Leads to Remote Code Execution
FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. A patch bypass vulnerability for CVE-2026-27636 in FreeScout 1.8.206 and earlier allows any authenticated user with file upload permissions to achieve Remote Code Execution (RCE) on the server by uploading a malicious .htaccess file using a zero-width space character prefix to bypass the security check. The vulnerability exists in the sanitizeUploadedFileName() function in app/Http/Helper.php. The function contains a Time-of-Check to Time-of-Use (TOCTOU) flaw where the dot-prefix check occurs before sanitization removes invisible characters. This vulnerability is fixed in 1.8.207.
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Frequently Asked Questions
What is the severity of CVE-2026-28289?
CVE-2026-28289 is classified as a high severity vulnerability due to its potential for remote code execution.
How can I mitigate CVE-2026-28289?
To mitigate CVE-2026-28289, upgrade to FreeScout version 1.8.207 or later, which contains a fix for this vulnerability.
Who is affected by CVE-2026-28289?
All users of FreeScout version 1.8.206 and earlier who are authenticated are affected by CVE-2026-28289.
What type of vulnerability is CVE-2026-28289?
CVE-2026-28289 is a patch bypass vulnerability that can lead to remote code execution.
What should I do if I cannot immediately update for CVE-2026-28289?
If you cannot update immediately for CVE-2026-28289, consider limiting access to the affected application and monitoring for suspicious activity.