CVE-2026-28289: FreeScout 1.8.206 Patch Bypass for CVE-2026-27636 via Zero-Width Space Character Leads to Remote Code Execution

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 34.9% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-03 · updated 2026-06-17
Weakness: CWE-434

Description

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.

Affected products

freescout-help-desk freescout: before 1.8.207 — fixed in 1.8.207

How to fix

Upgrade to a fixed version: freescout-help-desk freescout 1.8.207. Check the vendor advisory for mitigations.

References

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