# CVE-2026-40568: FreeScout Vulnerable to XSS via Mailbox Signature Due to Incomplete HTML Sanitization

> Authenticated users can inject malicious scripts into mailbox signatures, leading to session hijacking and data exfiltration when viewed by other agents.

- **Severity:** High 8.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 21 Apr 2026
- **Updated:** 21 Apr 2026
- **Also known as:** GHSA-w2f5-6wcv-677r

## What is CVE-2026-40568?

CVE-2026-40568 is a high-severity cross-site scripting vulnerability in freescout-help-desk freescout, published on 21 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

FreeScout is a free self-hosted help desk and shared mailbox. Versions prior to 1.8.213 have a stored cross-site scripting (XSS) vulnerability in the mailbox signature feature. The sanitization function `Helper::stripDangerousTags()` (`app/Misc/Helper.php:568`) uses an incomplete blocklist of only four HTML tags (`script`, `form`, `iframe`, `object`) and does not remove event handler attributes. When a mailbox signature is saved via `MailboxesController::updateSave()` (`app/Http/Controllers/MailboxesController.php:267`), HTML elements such as `<img>`, `<svg>`, and `<details>` with event handler attributes like `onerror` and `onload` pass through sanitization unchanged and are stored in the database. The signature is then rendered as raw HTML via the Blade `{!! !!}` tag in `editor_bottom_toolbar.blade.php:6` and re-inserted into the visible DOM by jQuery `.html()` at `main.js:1789-1790`, triggering the injected event handlers. Any authenticated user with the `ACCESS_PERM_SIGNATURE` (`sig`) permission on a mailbox -- a delegatable, non-admin permission -- can inject arbitrary HTML and JavaScript into the mailbox signature. The payload fires automatically, with no victim interaction, whenever any agent or administrator opens any conversation in the affected mailbox. This enables session hijacking (under CSP bypass conditions such as IE11 or module-weakened CSP), phishing overlays that work in all browsers regardless of CSP, and chaining to admin-level actions including email exfiltration via mass assignment and self-propagating worm behavior across all mailboxes. Version 1.8.213 fixes the issue.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-116 (Improper Encoding or Escaping of Output)

## Which versions are affected by CVE-2026-40568?


## How do I fix CVE-2026-40568?

No fix has been published for CVE-2026-40568 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-40568 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40568 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40568 and fix it if it is affected.

What it is: CVE-2026-40568 is a high-severity cross-site scripting vulnerability in freescout-help-desk freescout, published on 21 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40568 exists.

Affected product: freescout-help-desk freescout. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-40568/ (Markdown: https://insights.sbomify.com/CVE-2026-40568/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40568
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40568
- OSV: https://osv.dev/vulnerability/CVE-2026-40568

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40568/
Summaries are generated and may contain mistakes; the official description above is the record.