CVE-2025-40726: Nosto Reflected XSS Vulnerability

CVE-2025-40726 Overview

CVE-2025-40726 is a reflected Cross-Site Scripting (XSS) vulnerability affecting the /pages/search-results-page endpoint in Nosto. The flaw resides in the handling of the q GET request parameter, which is reflected into the response without proper sanitization or output encoding. Remote attackers can craft a malicious URL that, when visited by an authenticated or unauthenticated user, executes arbitrary JavaScript in the victim's browser session. The issue is tracked under CWE-79: Improper Neutralization of Input During Web Page Generation.

Critical Impact
Attackers can execute arbitrary JavaScript in a victim's browser via a crafted search URL, enabling session data theft, phishing overlays, and client-side account takeover.

Affected Products

Nosto search-results-page component
Deployments exposing the /pages/search-results-page endpoint
Storefronts integrating the vulnerable Nosto search functionality

Discovery Timeline

2025-06-16 - CVE-2025-40726 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-40726

Vulnerability Analysis

The vulnerability is a reflected XSS flaw in the Nosto search results page. The q query parameter, used to convey the user's search term, is embedded into the HTML response without adequate contextual output encoding. An attacker who convinces a victim to click a specially crafted link can execute arbitrary script content in the origin of the vulnerable site. Because the injection point sits on a customer-facing search page, exploitation typically requires only user interaction with a link, making phishing a viable delivery method. The vulnerability affects both confidentiality and integrity of client-side data within the browser context.

Root Cause

The root cause is improper neutralization of user-supplied input before it is written into the HTML response. The application reflects the q parameter into the search results markup without HTML entity encoding or a strict Content Security Policy that would neutralize inline script execution.

Attack Vector

Exploitation occurs over the network and requires user interaction. An attacker crafts a URL of the form https://<victim-site>/pages/search-results-page?q=<payload> where <payload> contains a JavaScript payload. When the victim opens the link, the payload executes in the browser under the vulnerable site's origin. Refer to the INCIBE Security Notice on XSS in Nosto for advisory details. No verified proof-of-concept code has been released publicly.

Detection Methods for CVE-2025-40726

Indicators of Compromise

Web server access logs containing requests to /pages/search-results-page with q parameter values that include <script>, onerror=, javascript:, or encoded variants such as %3Cscript%3E.
Unusually long or URL-encoded q parameter values inconsistent with legitimate search terms.
Referrer headers pointing to external phishing domains that lead users to the search endpoint.

Detection Strategies

Deploy web application firewall (WAF) signatures targeting reflected XSS payload patterns in the q parameter.
Correlate outbound browser telemetry with inbound HTTP requests to identify script execution originating from crafted search URLs.
Perform static and dynamic analysis of storefront templates to confirm whether q is rendered through an encoded template helper.

Monitoring Recommendations

Enable and centralize access logging for all /pages/search-results-page requests, retaining query strings for retrospective hunting.
Alert on repeated 200-response requests to the search endpoint containing HTML control characters in the q value.
Monitor customer support channels for reports of unexpected popups, redirects, or credential prompts on search pages.

How to Mitigate CVE-2025-40726

Immediate Actions Required

Apply the vendor-supplied fix from Nosto once available; consult the INCIBE advisory for the current remediation status.
Deploy WAF rules that block script tags and event-handler attributes in the q GET parameter on /pages/search-results-page.
Enforce a strict Content Security Policy that disallows inline scripts and restricts script sources to trusted origins.

Patch Information

At the time of publication, the NVD entry references the INCIBE-CERT advisory as the authoritative source. Organizations running Nosto integrations should contact the vendor for a fixed release version and apply it across all storefronts exposing the affected endpoint.

Workarounds

Sanitize and HTML-encode the q parameter at the reverse proxy or edge layer before it reaches the application.
Set X-XSS-Protection, X-Content-Type-Options: nosniff, and a restrictive Content-Security-Policy header on responses from /pages/search-results-page.
Temporarily restrict or disable the vulnerable search endpoint if a patch cannot be applied and business impact allows.

bash

# Example WAF rule (ModSecurity) blocking script payloads in the q parameter
SecRule ARGS:q "@rx (?i)(<script|onerror=|onload=|javascript:|<img|<svg)" \
    "id:1004072,phase:2,deny,status:403,log,\
     msg:'CVE-2025-40726 reflected XSS attempt in q parameter'"