Raw vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). EPSS scores by FIRST (EPSS SIG), generated by Empirical Security. Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-40568 is a high-severity Cross-site Scripting (CWE-79) vulnerability. Its CVSS base score is 8.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Browser Session Hijacking (T1185); ranked at the 34th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-40568 is a stored cross-site scripting (XSS) vulnerability affecting FreeScout, a free self-hosted help desk and shared mailbox application, in versions prior to 1.8.213. The issue resides in the mailbox signature feature, where the sanitization function Helper::stripDangerousTags() in app/Misc/Helper.php only blocks four HTML tags (script, form, iframe, object) and fails to remove event handler attributes. Consequently, elements like img, svg, and details with attributes such as onerror and onload bypass sanitization during saving via MailboxesController::updateSave() in app/Http/Controllers/MailboxesController.php, get stored in the database, and are rendered unsafely using Blade {!! !!} tags in editor_bottom_toolbar.blade.php and jQuery .html() in main.js, executing the injected code.
Any authenticated user with the delegatable ACCESS_PERM_SIGNATURE (sig) permission on a mailbox, which does not require admin privileges, can exploit this to inject arbitrary HTML and JavaScript into the signature. The payload executes automatically without user interaction whenever an agent or administrator opens any conversation in the affected mailbox. This allows session hijacking under conditions like CSP bypasses (e.g., IE11 or weakened CSP), phishing overlays effective across browsers, and chaining to higher-privilege actions such as email exfiltration through mass assignment or self-propagating worm-like behavior across mailboxes. The vulnerability carries a CVSS v3.1 score of 8.5 (AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N) and maps to CWE-79 and CWE-116.
The FreeScout security advisory (GHSA-w2f5-6wcv-677r) and release notes for version 1.8.213 detail the fix, implemented via commit 1d83e1cffb0bf8d109625313530b36b0f5910b3f, which addresses the incomplete sanitization. Security practitioners should upgrade to FreeScout 1.8.213 or later to mitigate the issue, as no additional workarounds are specified in the provided references.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-24169
Vulnerability Data
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…
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(`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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.1.2V1.3.2
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation can discover missing or incorrect input neutralization through targeted web-application tests.
Input validation directly enforces neutralization of untrusted data before it reaches web output generation.
Output filtering can catch or sanitize unneutralized script content before it is served to users.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly target introduction of XSS via coding standards/testing (mostly), yet the single broad outcome leaves many specific neutralization vectors unaddressed (partial).
Patching and EOL replacement can remediate known XSS instances in libraries or frameworks (partial) but do nothing to enforce input neutralization in application code (none).
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Secure-coding testing and automated code-analysis tools are applied to detect improper neutralization of script-related content during web-page generation.
Secure-coding standards, SAST scans and removal of insecure code samples together eliminate the failure to neutralize script content that produces cross-site scripting flaws.
Hardening callouts derived
DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.
- No fine-grained STIG row for CWE-116, a class-level weakness, and none of its children carries one either.