CVE-2026-13400
MediumCVSS 6.1Exploitation Probability (EPSS)
Low risk5th percentile - higher than 5% of all known CVEs
Summary
Simply Schedule Appointments is vulnerable to unauthenticated Stored Cross-Site Scripting in all versions up to and including 1.6.12.2. The root cause is a sanitization-ordering defect: the rendered notification content is decoded back into live HTML after it has already passed through the Simply Schedule Appointments WordPress plugin before 1.6.12.4's wp_kses_post() filter, so a double-encoded payload survives intake and is reintroduced as an executable element at render time.
Risk Assessment
An attacker can inject a malicious script that executes in other users' browsers, potentially stealing sessions or redirecting to malicious sites.
Recommendation
Update the Simply Schedule Appointments plugin to version 1.6.12.4 or later.
Other vulnerabilities in Simply Schedule Appointments
See all- CVE-2026-65508Critical
Unauthenticated SQL Injection vulnerability in Simply Schedule Appointments versions up to 1.6.12.10.
- CVE-2026-39493Critical
There is an unauthenticated SQL injection vulnerability in Simply Schedule Appointments versions up to 1.6.9.27.
- CVE-2026-65513High
Unauthenticated Cross Site Scripting (XSS) vulnerability in Simply Schedule Appointments plugin up to version 1.6.12.10. An unauthenticated attacker can inject malicious scripts.
- CVE-2026-15254Medium
The Simply Schedule Appointments WordPress plugin before version 1.6.12.11 does not perform a capability check on an administrative appointment-listing shortcode, and its per-user result scoping fails open for non-staff users. This allows users with the Contributor role and above to disclose all customers' appointment records, including names, email addresses, phone numbers and notes, across the whole site.
- CVE-2026-16540High
The Simply Schedule Appointments WordPress plugin before version 1.6.12.6 does not restrict a bulk appointment operation to the requester's own records. Unauthenticated users can retrieve personal data of all appointments and, on premium editions, permanently delete them.
- CVE-2026-59523Medium
The Simply Schedule Appointments WordPress plugin contains a missing authorization vulnerability that allows exploiting incorrectly configured access control security levels. This issue affects versions up to and including 1.6.11.11.
- CVE-2026-57812Medium
The Simply Schedule Appointments WordPress plugin contains a missing authorization vulnerability that allows exploiting incorrectly configured access control security levels. This issue affects versions up to and including 1.6.12.4.
- CVE-2026-57317High
The vulnerability allows an unauthenticated attacker to execute XSS scripts in the Simply Schedule Appointments plugin versions up to and including 1.6.12.2.
- CVE-2026-42384High
The Simply Schedule Appointments application versions below 1.6.11.2 have a vulnerability that allows unauthorized access to sensitive data.
- CVE-2026-39447High
Versions of Simply Schedule Appointments up to 1.6.10.6 are vulnerable to unauthenticated Cross Site Scripting (XSS). An attacker can exploit this vulnerability to inject malicious JavaScript code.
Original NVD description (English source)
Simply Schedule Appointments is vulnerable to unauthenticated Stored Cross-Site Scripting in all versions up to and including 1.6.12.2. The root cause is a sanitization-ordering defect: the rendered notification content is decoded back into live HTML after it has already passed through the Simply Schedule Appointments WordPress plugin before 1.6.12.4's wp_kses_post() filter, so a double-encoded payload survives intake and is reintroduced as an executable element at render time.