Summary
AVideo: HTML Injection in notifySubscribers.json.php Allows Platform-Branded Phishing Emails to Channel Subscribers
Impact
- Any authenticated uploader can weaponize the platform's own email infrastructure and brand (contact email, logo, site title) to deliver phishing content to their channel subscribers.
- Because the
From:address is the platform's canonical contact email and the template wraps the attacker content in the official logo and site title, recipients have no visible indication that the content originated from an uploader rather than the operator. Recipients who have previously received legitimate notifications from the same address are especially likely to trust the email. - Phishing payloads can include credential-stealing links mimicking password reset / account verification flows, tracking pixels that enumerate subscriber IPs and mail-client metadata, and CSS-based UI spoofing over the template.
- An admin account (
User::isAdmin()→$user_id = '') expands the blast radius to every subscriber record on the platform, not just the attacker's own subscribers. - Up to 10,000 recipients per request with no rate limiting, CAPTCHA, or unsubscribe link, so a compromised or malicious uploader can sustain large phishing campaigns at minimal cost, while the sending IP reputation is borne by the platform operator.
- A stolen uploader session (e.g., via an unrelated XSS or token leak) is sufficient to mount the attack; no additional credentials or admin access are required.
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-2026-43876 has a CVSS score of 6.4 (Medium). The vector is network-reachable, low privileges required, and no user interaction. 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.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Sanitize or encode $_POST['message'] before it reaches PHPMailer::msgHTML(). Options, in order of preference:
Reject HTML outright and force plain text. In
objects/notifySubscribers.json.php:$message = $_POST['message'] ?? ''; // Strip all HTML; allow only newlines / plain text. $message = strip_tags($message); $message = nl2br(htmlspecialchars($message, ENT_QUOTES | ENT_HTML5, 'UTF-8'));Or allow a very restricted subset using a proven HTML sanitizer (e.g.
HTMLPurifierwith a minimal whitelist:p, br, strong, em, a[href|title], ul, ol, li), and forbid<script>,<style>, inline event handlers,<img>,<iframe>,data:/javascript:URIs, and framework-style template tokens.Additionally remove the
preg_match("/html>/i", $message)short-circuit atobjects/functionsMail.php:268-270, which lets a caller replace the entire email body by including a<html>tag. The template should always be applied.Defense in depth:
- Require a real anti-CSRF token on this endpoint (e.g.
validateCSRF()with a per-session token in a header or POST field), and drop the Referer-onlyforbidIfIsUntrustedRequestas the sole protection. - Require
User::isAdmin()to notify subscribers from accounts not scoped to a channel; for non-admin uploaders, make theFromdisplay name clearly attribute the message to the uploader ("{uploaderName} via {siteTitle} <contact@site>"already works for non-system senders inobjects/functionsMail.php:130-134, apply the same attribution to subscriber notifications). - Enforce per-account and per-IP rate limits on
notifySubscribers.json.php(e.g. one broadcast per account per N hours, max M recipients per day). - Include a List-Unsubscribe header and a per-recipient unsubscribe link.
- Add a preview + confirmation step before dispatch.
- Require a real anti-CSRF token on this endpoint (e.g.
Frequently Asked Questions
- What is CVE-2026-43876? CVE-2026-43876 is a medium-severity cross-site scripting (XSS) vulnerability in wwbn/avideo (composer), affecting versions <= 29.0. 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.
- How severe is CVE-2026-43876? CVE-2026-43876 has a CVSS score of 6.4 (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.
- Which versions of wwbn/avideo are affected by CVE-2026-43876? wwbn/avideo (composer) versions <= 29.0 is affected.
- Is there a fix for CVE-2026-43876? No fixed version is listed for CVE-2026-43876 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2026-43876 exploitable, and should I be worried? Whether CVE-2026-43876 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
- What actually determines whether CVE-2026-43876 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.
- How do I fix CVE-2026-43876? 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.