CVE-2026-13441: EventPrime WordPress Plugin Stored XSS Vulnerability – HIGH Severity

Technical summary

The vulnerability is a Stored XSS issue (CWE-79) in the EventPrime plugin affecting versions up to and including 4.3.4.2. The 'new_event_type_background_color' parameter fails to properly sanitize user input and does not adequately escape output in the frontend event submission form. This allows authenticated attackers with custom-level access or higher to inject arbitrary JavaScript. Exploitation is simplified when the 'allow_submission_by_anonymous_user' configuration is enabled, which permits unauthenticated form submissions. The injected payload persists in the plugin's database and executes client-side each time the stored page is rendered, making it a persistent threat rather than a reflected attack.

Business impact

A successful exploit could lead to session hijacking of website administrators or event organizers, credential theft from event attendees, malware distribution to site visitors, or defacement of event pages. For sites relying on EventPrime for ticket sales, this creates fraud and reputation risks. Multi-site WordPress installations could amplify the blast radius if the plugin is network-activated. The vulnerability requires user interaction (visiting the compromised page) but not sophisticated social engineering, making it a practical threat in environments with loose access controls or where guest submissions are broadly enabled.

Affected systems

The EventPrime – Events Calendar, Bookings and Tickets WordPress plugin is affected in all versions up to and including 4.3.4.2. The vulnerability manifests only if the plugin is installed and activated; the attack surface depends on configuration. Sites with guest submissions enabled are at highest risk and require no credentials for initial exploitation. Sites with guest submissions disabled still face risk from any user with subscriber-level or higher WordPress privileges who can submit event types via the backend form.

Exploitability

This vulnerability is straightforward to exploit. With guest submissions enabled, attackers can directly access the frontend event submission form without authentication and inject malicious CSS or JavaScript in the color field using basic encoding or obfuscation techniques. No special tooling is required; a browser and understanding of XSS payloads suffice. The attack is deterministic—payloads reliably persist and execute—making it highly reliable for an attacker. The CVSS score of 7.2 (HIGH) reflects the ease of exploitation, network accessibility, and potential for cross-site impact, though the complexity remains low because exploitation does not require special conditions beyond the configuration state.

Remediation

Update the EventPrime plugin to a patched version released after 4.3.4.2; verify against the official EventPrime vendor advisory for the specific version number. The patch should implement proper input sanitization (stripping or escaping HTML/JavaScript in color parameters) and output escaping (using WordPress functions like esc_attr() and wp_kses_post() where appropriate). As an interim mitigation, disable the 'Guest Submissions' / 'allow_submission_by_anonymous_user' setting to restrict event type submissions to authenticated subscribers and above, then implement a role-based review process for new event types before they appear publicly. If the plugin cannot be updated immediately, consider restricting access to event submission forms via Web Application Firewall (WAF) rules or removing the plugin if it is not mission-critical.

Patch guidance

Check the EventPrime plugin repository or vendor website for a security update addressing CVE-2026-13441. Patches typically arrive within 1–2 weeks after public disclosure. When available, the update will be marked as a security release. In WordPress admin, navigate to Plugins > Updates and install the new version. Before deployment to production, test the update on a staging environment to ensure compatibility with custom event templates and third-party integrations. Review the changelog to confirm that input sanitization and output escaping have been applied to the 'new_event_type_background_color' parameter. If using managed WordPress hosting, the update may be applied automatically.

Detection guidance

Monitor WordPress error logs and web server access logs for event submission requests containing encoded HTML entities or script tags in the 'new_event_type_background_color' parameter. Look for patterns like '%3Cscript%3E', 'javascript:', or 'onerror=' in POST requests to the event submission endpoint. Use WordPress security plugins (e.g., Wordfence, Sucuri) to scan for stored XSS payloads in the database, specifically in the event type metadata tables. Review the plugin's event type records for suspicious color values that do not conform to valid hex or RGB color syntax. If a WAF is in place, create signatures to block requests with unescaped angle brackets or JavaScript keywords in color parameters.

Why prioritize this

Although CVE-2026-13441 is not currently listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, it presents a HIGH-severity risk due to its ease of exploitation, low barrier to entry (no authentication if guest submissions are enabled), and broad WordPress ecosystem adoption. EventPrime's role in handling event registrations and payments means compromised sites may expose customer data. The vulnerability is post-authentication in some configurations but pre-authentication in others, widening its threat model. Organizations running EventPrime with guest submissions enabled should treat this as urgent; those with guest submissions disabled should prioritize it within the next 30 days of patch availability.

Risk score, explained

The CVSS 3.1 score of 7.2 reflects: (1) Network-accessible attack vector with no special requirements; (2) Low attack complexity—standard XSS injection techniques apply; (3) No privileges required (PR:N) when guest submissions are enabled; (4) No user interaction required for payload delivery (UI:N)—the attack succeeds on form submission; (5) Changed scope (S:C)—the injected script can affect other users' browsers; (6) Low confidentiality impact (C:L)—session tokens or cookies may be stolen; (7) Low integrity impact (I:L)—page content can be modified; (8) No availability impact (A:N)—the attack does not crash services. The HIGH severity appropriately flags the post-authentication variant and the ease of exploitation; real-world risk is elevated for sites with guest submissions enabled.

Frequently asked questions