CVE-2025-55420

HighPublic PoC

Published: 21 August 2025

Published

21 August 2025

Modified

09 September 2025

KEV Added

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Patch

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CVSS Score 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

EPSS Score 0.0019 40.5th percentile

Risk Priority 18 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2025-55420 is a high-severity Cross-site Scripting (CWE-79) vulnerability in Foxcms Foxcms. Its CVSS base score is 8.8 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 40.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-15 (Information Output Filtering).

Threat & Defense at a Glance

What attackers do: exploitation maps to Exploit Public-Facing Application (T1190) and 1 other technique. What defenders deploy: see the NIST 800-53 controls recommended below.

Threat & Defense Details

Mitigating Controls (NIST 800-53 r5)AI

SI-15 Information Output Filtering good match

prevent

SI-15 directly prevents reflected XSS by requiring filtering of HTML outputs to sanitize crafted scripts reflected from GET requests in /index.php responses.

SI-10 Information Input Validation good match

prevent

SI-10 enforces validation of GET request inputs to block malicious scripts before they are processed and reflected by FoxCMS /index.php.

SI-2 Flaw Remediation good match

prevent

SI-2 mandates identification and remediation of the specific flaw in FoxCMS v1.2.6 that allows unsanitized script reflection, preventing exploitation.

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.

attack.mitre.org →

T1059.007 JavaScript Execution

Adversaries may abuse various implementations of JavaScript for execution.

attack.mitre.org →

Why these techniques?

Reflected XSS in public-facing web app directly enables exploitation via T1190 and arbitrary JS execution via T1059.007.

Confidence: HIGH · MITRE ATT&CK Enterprise v18.1

NVD Description

A Reflected Cross Site Scripting (XSS) vulnerability was found in /index.php in FoxCMS v1.2.6. When a crafted script is sent via a GET request, it is reflected unsanitized into the HTML response. This permits execution of arbitrary JavaScript code when…

a logged-in user submits the malicious input.

Deeper analysisAI

CVE-2025-55420 is a reflected Cross-Site Scripting (XSS) vulnerability in the /index.php component of FoxCMS version 1.2.6. The flaw occurs when a crafted script is sent via a GET request, which is reflected unsanitized into the HTML response. This enables execution of arbitrary JavaScript code when a logged-in user submits or processes the malicious input. The vulnerability is associated with CWE-79 and carries a CVSS v3.1 base score of 8.8 (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H).

Any network-accessible attacker can exploit this vulnerability with low attack complexity and no privileges required, though it depends on user interaction from a logged-in victim. By tricking the target into accessing a malicious URL or submitting crafted input, the attacker can execute arbitrary JavaScript in the victim's browser context within the FoxCMS application. This could lead to high impacts, including theft of session data, account takeover, or further site compromise, given the elevated confidentiality, integrity, and availability effects.

Mitigation details are available in the referenced advisory at https://www.notion.so/FoxCMS-V1-2-6-Reflected-XSS-in-index-php-2222b2fd021080589d27ef8e1b9ebd86?source=copy_link, published on 2025-08-21.