CVE-2026-42877

FacturaScripts vulnerable to stored XSS via product reference in sales/purchases

Although session cookies (fsLogkey, fsNick) have the HttpOnly flag set and cannot be read directly via document.cookie, the injected script runs in the victim's authenticated browser context, meaning the attacker can make arbitrary authenticated requests on their behalf, create new admin users via AJAX POST to /EditUser, exfiltrate any business data visible in the DOM, or redirect the user to an external site. The most critical scenario is privilege escalation: a low-privilege employee with only warehouse
access can execute JavaScript in an administrator's session without knowing their password.

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-42877 has a CVSS score of 5.4 (Medium). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

Apply htmlspecialchars() with ENT_QUOTES before inserting referencia into the onclick attribute in both affected files.

Core/Lib/AjaxForms/SalesModalHTML.php

// Before (vulnerable):
$tbody .= '<tr onclick="return salesFormAction(\'add-product\', \''
    . $row['referencia']
    . '\');">';

// After (safe):
$tbody .= '<tr onclick="return salesFormAction(\'add-product\', \''
    . htmlspecialchars($row['referencia'], ENT_QUOTES, 'UTF-8')
    . '\');">';

Core/Lib/AjaxForms/PurchasesModalHTML.php

Apply the same change to the equivalent line.

Why ENT_QUOTES is required: ENT_QUOTES encodes both " and ' characters. This ensures that ' is stored as ' and, critically, remains ' after innerHTML assignment, because htmlspecialchars produces a form that the HTML parser does not decode back into a raw quote inside a JS string context.

Alternative mitigation: replace innerHTML with innerText or a DOM-based rendering approach that never parses injected strings as HTML. This would eliminate the entire class of HTML-injection-via-innerHTML vulnerabilities in the sales and purchases
forms.

1. What is CVE-2026-42877? CVE-2026-42877 is a medium-severity cross-site scripting (XSS) vulnerability in facturascripts/facturascripts (composer), affecting versions <= 2025.92. No fixed version is listed yet. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-42877? CVE-2026-42877 has a CVSS score of 5.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of facturascripts/facturascripts are affected by CVE-2026-42877? facturascripts/facturascripts (composer) versions <= 2025.92 is affected.
4. Is there a fix for CVE-2026-42877? No fixed version is listed for CVE-2026-42877 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-42877 exploitable, and should I be worried? Whether CVE-2026-42877 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-42877 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-42877? No fixed version is listed yet. In the interim: Validate and encode untrusted input before rendering it as HTML. Applying a Content Security Policy reduces the impact if encoding is bypassed.