CVE-2026-28289CWE-434

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

Critical · published March 3, 2026

CVSS v3.1
10.0
EPSS
3%
Percentile
85.9
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
10.0 · CRITICAL
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
CVSS v4.0
Not supplied
EPSS
0.02720 · 85.9th percentile
Weakness
CWE-434 · Unrestricted Upload of File with Dangerous Type
Published
2026-03-03T22:59Z
EPSS history
Timeline
  • 25 SEP 03:25Z
    EPSS moved 31% → 3%
    epss
  • 03 MAR 22:59Z
    FreeScout 1.8.206 Patch Bypass for CVE-2026-27636 via Zero-Width Space Character Leads to Remote Code Execution
    cvelistv5