Bookly Plugin Stored XSS via Unprotected AJAX Handler

The Online Scheduling and Appointment Booking System – Bookly plugin for WordPress is vulnerable to Stored Cross-Site Scripting via bookly_speed_up_update_addons AJAX action in all versions up to, and including, 27.7 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page. The injection point is the bookly_speed_up_update_addons AJAX action, which is registered as wp_ajax_nopriv_* and therefore reachable without authentication; the payload is stored verbatim in the bookly_log.details column when a request is submitted without a valid signature, and executes when an administrator later views the Diagnostics → Logs page.

Casky was already ahead

This CVE exploits attack patterns that Casky's 322matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.

Analysis

The Bookly WordPress plugin contains a stored cross-site scripting (XSS) vulnerability in the bookly_speed_up_update_addons AJAX action that allows unauthenticated attackers to inject malicious scripts into web pages. This vulnerability affects all versions up to 27.7 and exploits insufficient input sanitization and output escaping—classic CWE-79 flaws that create persistent threats. Any WordPress site using Bookly for appointment scheduling is vulnerable, meaning thousands of businesses relying on this plugin for client-facing booking systems could be compromised without requiring user authentication.

Casky's 322 mapped security skills detect this attack pattern by correlating MITRE ATT&CK techniques TA0001 (Initial Access) and TA0043 (Reconnaissance) with Claude's extended reasoning capabilities. When analyzing web traffic and plugin behavior, practitioners using Casky would identify suspicious AJAX requests to bookly_speed_up_update_addons endpoints containing script payloads, detect stored malicious content in WordPress post metadata or plugin options tables, and observe reflected script execution in user sessions. The platform flags unescaped output patterns in plugin callbacks, recognizes the reconnaissance phase where attackers probe for Bookly presence, and traces how initial access through unauthenticated AJAX handlers enables persistent code injection—enabling security teams to prioritize patch deployment and audit compromised WordPress installations before attackers achieve lateral movement or data exfiltration.

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Casky Risk Score

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EPSS Probability

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Shodan Exposure

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GreyNoise Signal

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Composite risk scoring from EPSS, CISA KEV, Shodan, and GreyNoise — 21 security APIs correlated into a single Casky Risk Score. Coming in Casky Pro. Join early access →

322 Casky skills cover this attack pattern

These skills use Claude AI's reasoning model to surface findings in the same attack categories as CVE-2026-13424.

Abuse of Public-Facing API: Mobile API Abuse

mobile security · low

Run

abusing-dpapi-for-credential-access

red teaming · high

Run

abusing-shadow-credentials-for-privesc

red teaming · high

Run

MITRE ATT&CK Techniques

TA0001 TA0043

Investigate the attack patterns behind CVE-2026-13424

Casky has 322 skills that investigate the attack patterns behind CVE-2026-13424. Run one and get CVSS-scored findings in 3 minutes.

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