CVE-2026-40497 FreeScout Vulnerable to CSS Injection via Stored Style Tag in Mailbox Signature (CSRF Token Exfiltration)
Attackers can inject CSS to steal CSRF tokens, enabling privilege escalation from agent to admin in FreeScout help desk.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-40497?
CVE-2026-40497 is a high-severity cross-site scripting vulnerability in freescout-help-desk freescout, published on 21 Apr 2026. An attacker needs administrator access to exploit it, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-79
Which versions are affected by CVE-2026-40497?
It affects 1 product.
Products include Freescout Freescout.
How do I fix CVE-2026-40497?
No fix has been published for CVE-2026-40497 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-40497 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40497 exists.
Other vulnerabilities in freescout-help-desk freescout
- CVE-2026-28289 FreeScout 1.8.206 Patch Bypass for CVE-2026-27636 via Zero-Width Space Character Leads to Remote Code Execution
- CVE-2026-27637 FreeScout's Predictable Authentication Token Enables Account Takeover
- CVE-2026-32754 FreeScout: Stored XSS via Unescaped Email Template Rendering ({!! $thread->body !!})
- CVE-2024-29185 FreeScout OS Command Injection vulnerability
- CVE-2026-40498 FreeScout has Authentication Bypass and Information Disclosure in SystemController via /system/cron
Sources
Also known as GHSA-fh99-wr77-pxq3.