CVE-2026-28289

Published Mar 3, 2026

Last updated 2 months ago

CVSS critical 10.0

Overview

AI description

Automated description summarized from trusted sources.

CVE-2026-28289 is a Remote Code Execution (RCE) vulnerability impacting FreeScout, a help desk and shared inbox application built with the Laravel framework. This flaw, also known as "Mail2Shell," is a patch bypass for a previously identified vulnerability (CVE-2026-27636). It allows an attacker to execute arbitrary code on the server by exploiting a filename sanitization bypass during file uploads. The vulnerability specifically involves the upload of malicious `.htaccess` files. FreeScout's sanitization logic, intended to prevent dangerous file uploads, can be circumvented by prepending a zero-width Unicode character to the filename. This bypasses validation checks, allowing the `.htaccess` file to be saved and subsequently used to execute arbitrary commands, potentially through a PHP webshell. In some scenarios, this can be triggered without authentication or user interaction by sending a specially crafted email to a FreeScout mailbox.

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.
Source
security-advisories@github.com
NVD status
Analyzed
Products
freescout

Risk scores

CVSS 3.1

Type
Primary
Base score
8.1
Impact score
5.9
Exploitability score
2.2
Vector string
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Severity
HIGH

Weaknesses

security-advisories@github.com
CWE-434

Social media

Hype score
Not currently trending

  1. Metasploit Framework is here with 5 new modules! Exploits for FreeScout (CVE-2026-28289) and Grav CMS (CVE-2025-50286) RCEs, plus a generic HTTP command execution module and a new Windows persistence technique. We also have a slew of bug fixes and enhancements including SOCKS

    @metasploit

    3 Apr 2026

    4401 Impressions

    10 Retweets

    35 Likes

    7 Bookmarks

    1 Reply

    0 Quotes

Configurations

Related CVEs

  1. FreeScout is a free self-hosted help desk and shared mailbox. Prior to version 1.8.213, FreeScout's linkify() function in app/Misc/Helper.php converts plain-text URLs in email bodies into HTML anchor tags without escaping double-quote characters (") in the URL. HTMLPurifier (called first via getCleanBody()) preserves literal " characters in text nodes. linkify() then wraps URLs including those " chars inside an unescaped href="..." attribute, breaking out of the href and injecting arbitrary HTML attributes. Version 1.8.213 fixes the issue.•CVE-2026-40565
  2. FreeScout is a free self-hosted help desk and shared mailbox. Prior to version 1.8.213, an unauthenticated attacker can access diagnostic and system tools that should be restricted to administrators. The /system/cron endpoint relies on a static MD5 hash derived from the APP_KEY, which is exposed in the response and logs. Accessing these endpoints reveals sensitive server information (Full Path Disclosure), process IDs, and allows for Resource Exhaustion (DoS) by triggering heavy background tasks repeatedly without any rate limiting. The cron hash is generated using md5(APP_KEY . 'web_cron_hash'). Since this hash is often transmitted via GET requests, it is susceptible to exposure in server logs, browser history, and proxy logs. Furthermore, the lack of rate limiting on these endpoints allows for automated resource exhaustion (DoS) and brute-force attempts. Version 1.8.213 fixes the issue.•CVE-2026-40498
  3. FreeScout is a free self-hosted help desk and shared mailbox. Prior to version 1.8.213, FreeScout's `Helper::stripDangerousTags()` removes `<script>`, `<form>`, `<iframe>`, `<object>` but does NOT strip `<style>` tags. The mailbox signature field is saved via POST /mailbox/settings/{id} and later rendered unescaped via `{!! $conversation->getSignatureProcessed([], true) !!}` in conversation views. CSP allows `style-src * 'self' 'unsafe-inline'`, so injected inline styles execute freely. An attacker with access to mailbox settings (admin or agent with mailbox permission) can inject CSS attribute selectors to exfiltrate the CSRF token of any agent/admin who views a conversation in that mailbox. With the CSRF token, the attacker can perform any state-changing action as the victim (create admin accounts, change email/password, etc.) — privilege escalation from agent to admin. This is the result of an incomplete fix of GHSA-jqjf-f566-485j. That advisory reported XSS via mailbox signature. The fix applied `Helper::stripDangerousTags()` to the signature before saving. However, `stripDangerousTags()` only removes `script`, `form`, `iframe`, and `object` tags — it does NOT strip `<style>` tags, leaving CSS injection possible. Version 1.8.213 contains an updated fix.•CVE-2026-40497
  4. FreeScout is a free self-hosted help desk and shared mailbox. Prior to version 1.8.213, attachment download tokens are generated using a weak and predictable formula: `md5(APP_KEY + attachment_id + size)`. Since attachment_id is sequential and size can be brute-forced in a small range, an unauthenticated attacker can forge valid tokens and download any private attachment without credentials. Version 1.8.213 fixes the issue.•CVE-2026-40496
  5. FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. Prior to 1.8.212, FreeScout does not take the limit_user_customer_visibility parameter into account when merging customers. This vulnerability is fixed in 1.8.212.•CVE-2026-39384

References

Sources include official advisories and independent security research.