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Cross-site Scripting (XSS)Weakness · CWE-79

CVE-2026-40568

HIGH · 8.5 CVSS v3.1 Published 2026-04-21
Patch available
A vendor patch is available. No clean upgrade release — apply the published patch.
See remediation →
91/100
Remediation priority · Urgent
Remotely reachable Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-79

Untrusted input is placed into a web page without being neutralised, so an attacker's markup or script executes in another user's browser. That can hijack sessions, capture keystrokes, or silently perform actions as the victim. Fixing it properly means context-aware output encoding everywhere data meets HTML, backed by a content-security policy as a second line of defence.

General guidance for the cross-site scripting (xss) class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Patch available Apply the vendor patch
Vendor patch github.com →
Recommended fix High confidence

1.8.213

  1. 1. Back up your current FreeScout installation and database before upgrading.
  2. 2. Upgrade FreeScout to version 1.8.213 or later.
  3. 3. Verify the upgrade was successful by checking the version in the admin panel.
  4. 4. Confirm the `Helper::stripDangerousTags()` function now properly sanitizes event handler attributes and additional HTML tags.

Generated from the published advisory — verify against the referenced sources before acting.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-40568 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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