CVE-2026-40568— FreeScout Vulnerable to XSS via Mailbox Signature Due to Incomplete HTML Sanitization
Quick assessment
Affected
freescout-help-desk freescout
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
FreeScout是FreeScout公司的一个使用 PHP（Laravel 框架）构建的超轻量级且功能强大的免费开源帮助台和共享收件箱。 FreeScout 1.8.213之前版本存在安全漏洞，该漏洞源于邮箱签名功能中的清理函数Helper::stripDangerousTags使用不完整的阻止列表且未移除事件处理程序属性，可能导致具有ACCESS_PERM_SIGNATURE权限的认证用户注入任意HTML和JavaScript，触发会话劫持或钓鱼攻击。
Possible ATT&CK Techniques 3 AI
T1001 · Data Obfuscation T1059 · Command and Scripting Interpreter T1189 · Drive-by Compromise
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I. Basic Information for CVE-2026-40568
Vulnerability Information
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Vulnerability Title
FreeScout Vulnerable to XSS via Mailbox Signature Due to Incomplete HTML Sanitization
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
FreeScout 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
FreeScout是FreeScout公司的一个使用 PHP（Laravel 框架）构建的超轻量级且功能强大的免费开源帮助台和共享收件箱。 FreeScout 1.8.213之前版本存在安全漏洞，该漏洞源于邮箱签名功能中的清理函数Helper::stripDangerousTags使用不完整的阻止列表且未移除事件处理程序属性，可能导致具有ACCESS_PERM_SIGNATURE权限的认证用户注入任意HTML和JavaScript，触发会话劫持或钓鱼攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| freescout-help-desk | freescout | < 1.8.213 | - |
|
II. Public POCs for CVE-2026-40568
| # | POC Description | Source Link | Shenlong Link |
|---|
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Vendor Advisories for CVE-2026-40568 (1)
Vendor Pages for CVE-2026-40568 (1)
Same Patch Batch · freescout-help-desk · 2026-04-21 · 20 CVEs total
| CVE-2026-41193 | 9.1 CRITICAL | FreeScout has Zip Slip path traversal in module installation that allows arbitrary file wr |
| CVE-2026-40569 | 9.0 CRITICAL | FreeScout's Mass Assignment in Mailbox Connection Settings Enables Silent Email Exfiltrati |
| CVE-2026-40497 | 8.1 HIGH | FreeScout Vulnerable to CSS Injection via Stored Style Tag in Mailbox Signature (CSRF Toke |
| CVE-2026-40589 | 7.6 HIGH | FreeScout has Customer Edit Cross-Mailbox Email Takeover |
| CVE-2026-41190 | 7.1 HIGH | FreeScout has assigned-only visibility bypass via save_draft that allows hidden conversati |
| CVE-2026-41189 | 7.1 HIGH | FreeScout has assigned-only visibility bypass that allows editing hidden customer-authored |
| CVE-2026-41191 | 7.1 HIGH | FreeScout's signature only mailbox permission allows unauthorized mailbox chat setting cha |
| CVE-2026-40591 | 7.1 HIGH | FreeScout: Improper Authorization in Phone Conversation Creation Enables Cross-Mailbox Hid |
| CVE-2026-41192 | 7.1 HIGH | FreeScout's client-controlled attachment IDs allow deletion of existing conversation attac |
| CVE-2026-40565 | 6.1 MEDIUM | FreeScout has Stored XSS / CSS Injection via linkify() — Unescaped URL in Anchor href |
| CVE-2026-40592 | 5.9 MEDIUM | FreeScout's cross-user undo reply allows mailbox peers to recall another agent's outbound |
| CVE-2026-40567 | 5.8 MEDIUM | FreeScout has HTML Injection in Outgoing Emails via Unsanitized Customer Name in Signature |
| CVE-2026-41194 | 5.4 MEDIUM | FreeScout's Mailbox OAuth disconnect uses a state-changing GET and is CSRFable |
| CVE-2026-41183 | 4.3 MEDIUM | FreeScout allows non-folder conversation queries to disclose assigned-only hidden conversa |
| CVE-2026-40590 | 4.3 MEDIUM | FreeScout's Customer AJAX Create Modifies Hidden Existing Customer |
| CVE-2026-40566 | 4.1 MEDIUM | FreeScout vulnerable to SSRF via IMAP/SMTP Connection Test Endpoints |
| CVE-2026-40570 | FreeScout's Missing Authorization in load_customer_info Allows Any Authenticated User to A | |
| CVE-2026-40498 | FreeScout has Authentication Bypass and Information Disclosure in SystemController via /sy | |
| CVE-2026-40496 | FreeScout has Predictable Attachment Token that Allows Unauthenticated Private File Downlo |
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