Raw vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:NSummary
CVE-2026-40497 is a high-severity Cross-site Scripting (CWE-79) vulnerability in Freescout Freescout. Its CVSS base score is 8.1 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Browser Session Hijacking (T1185); ranked at the 16th 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-2026-40497 is a CSS injection vulnerability in FreeScout, a free self-hosted help desk and shared mailbox application. In versions prior to 1.8.213, the `Helper::stripDangerousTags()` function removes dangerous HTML tags such as `<script>`, `<form>`, `<iframe>`, and `<object>`, but fails to strip `<style>` tags. This allows malicious CSS to be injected via the mailbox signature field, which is saved through POST /mailbox/settings/{id} and rendered unescaped using `{!! $conversation->getSignatureProcessed([], true) !!}` in conversation views. The Content Security Policy permits `style-src * 'self' 'unsafe-inline'`, enabling execution of injected inline styles. The issue stems from an incomplete fix for GHSA-jqjf-f566-485j, which addressed XSS in the same field but overlooked CSS injection. The vulnerability has a CVSS v3.1 score of 8.1 (AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:N) and is associated with CWE-79 (Cross-site Scripting).
An attacker with access to mailbox settings—such as an admin or agent with mailbox permissions—can inject CSS attribute selectors into the signature. When another agent or admin views a conversation in that mailbox, the injected CSS exfiltrates their CSRF token. Armed with the victim's CSRF token, the attacker can perform any state-changing action on their behalf, including creating admin accounts, changing email addresses or passwords, and achieving privilege escalation from agent to admin.
Advisories and patches recommend updating to FreeScout version 1.8.213, which includes an updated fix via commit 5aa8d633216f65995e80a7d4a921b784acc94df4. Details are available in the GHSA advisory GHSA-fh99-wr77-pxq3 and the release notes.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-24052
Vulnerability Data
FreeScout is a free self-hosted help desk and shared mailbox. Prior to version 1.8.213, FreeScout's `Helper::stripDangerousTags()` removes `<script>`, `<form>`, `<iframe>`, `<object>` but does NOT strip `<style>` tags. The mailbox signature field is saved via POST /mailbox/settings/{id} and later rendered unescaped…
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via `{!! $conversation->getSignatureProcessed([], true) !!}` in conversation views. CSP allows `style-src * 'self' 'unsafe-inline'`, so injected inline styles execute freely. An attacker with access to mailbox settings (admin or agent with mailbox permission) can inject CSS attribute selectors to exfiltrate the CSRF token of any agent/admin who views a conversation in that mailbox. With the CSRF token, the attacker can perform any state-changing action as the victim (create admin accounts, change email/password, etc.) — privilege escalation from agent to admin. This is the result of an incomplete fix of GHSA-jqjf-f566-485j. That advisory reported XSS via mailbox signature. The fix applied `Helper::stripDangerousTags()` to the signature before saving. However, `stripDangerousTags()` only removes `script`, `form`, `iframe`, and `object` tags — it does NOT strip `<style>` tags, leaving CSS injection possible. Version 1.8.213 contains an updated fix.
- 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.
Knowledge exchange on emerging attack techniques and patches reduces the likelihood that cross-site scripting flaws remain unaddressed in deployed applications.
Operational indicators of compromise for web-application attacks can be incorporated into WAF or input-filtering rules, lowering the likelihood that unsanitized data reaches the browser.
Requiring language-specific secure-coding standards and automated scanning during the SDLC catches missing output encoding or improper neutralization of untrusted data before the software reaches production.
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.
Webpage malware scanning and block-listing of known malicious sites reduce the likelihood that reflected or stored script payloads reach a user’s browser.