Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2023-3521 is a medium-severity Cross-site Scripting (CWE-79) vulnerability in Fossbilling Fossbilling. Its CVSS base score is 6.1 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Protocol or Service Impersonation (T1001.003); ranked in the top 41% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
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-2023-3521 is a reflected cross-site scripting vulnerability (CWE-79) affecting the FOSSBilling open-source billing application in versions prior to 0.5.4. The flaw resides in user-supplied input handling that is reflected back to the browser without adequate sanitization, allowing malicious scripts to execute in the context of the application origin.
An unauthenticated remote attacker can exploit the issue by crafting a URL containing a malicious payload and inducing a victim to click it. Successful exploitation results in arbitrary JavaScript execution within the victim's session, with the potential to read sensitive data or perform actions on behalf of the user due to the changed scope noted in the CVSS vector.
Public references point to a fix merged in commit 5eb516d4ebcb764db1b2edf9c8d0539e76ebde52 on the FOSSBilling repository; administrators are advised to upgrade to version 0.5.4 or later. The associated Huntr.dev report documents the same remediation path.
The EPSS score has remained flat at 0.1896 with no material increase observed after disclosure.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2023-44178
Vulnerability Data
Cross-site Scripting (XSS) - Reflected in GitHub repository fossbilling/fossbilling prior to 0.5.4.
- 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
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Penetration testing submits XSS payloads to web applications, detecting cross-site scripting flaws for subsequent remediation.
Validates web inputs to reject script-related content that could produce XSS.
Output validation against expected content can reject or sanitize script content in generated web pages, reducing XSS exploitability.
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.
A.5.6 only promotes membership in groups to improve knowledge, receive alerts, and share information; it performs no action that stops XSS exploitation (or even the underlying neutralization defect) and is a pure dependency for other controls per the owner's labeling rule.