CVE-2026-8840

Booking calendar, Appointment Booking System <= 3.2.36 - Missing Authorization to Unauthenticated Arbitrary Modification via wpdevart_payment AJAX Action

The Booking calendar, Appointment Booking System plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 3.2.36. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for unauthenticated attackers to mark arbitrary reservations as paid or completed, cancel legitimate payments, auto-approve reservations, and trigger transactional booking emails by writing attacker-supplied payment status and transaction data directly into the payments table. The auto-approval of reservations is only triggered when the 'enable_psuccess_approval' site option is enabled, but payment status manipulation and email dispatch are exploitable regardless of that setting.

We have discovered 655 live websites that are affected by CVE-2026-8840.

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Affected Software

Product  Booking Calendar
Category Wordpress Plugins
Vulnerable Domains655 live websites (100% of Booking Calendar install base)
Vulnerable Versions
  • from 0 through 3.2.36
Vulnerable Versions Count5 versions ( 100% of all versions)


Common Weakness Enumeration

CWE-862 Missing Authorization



Details

  • Published - Aug 15, 2026
  • Updated - Aug 17, 2026

Credits

  • Raihan Adi Arba (finder)

Website Distribution by Country

Number of websites using CVE-2026-8840
United States145 websites


Germany82 websites
GB45 websites
France40 websites
Italy31 websites
Netherlands27 websites
Spain26 websites
Poland20 websites
Belgium16 websites
Switzerland16 websites

Website Distribution by TLD

Number of websites using CVE-2026-8840
.com252 websites
.de57 websites
.fr32 websites
.co.uk26 websites
.nl24 websites
.it24 websites
.org22 websites
.pl19 websites
.cz14 websites
.net14 websites

Vulnerable Versions

Vulnerable versions are highlighted in red

Websites affected by CVE-2026-8840

Top websites that are affected by CVE-2026-8840. Please click on the "Contact us" link to get more information.
DomainCountryRankContacts
***.cz Czech Republic***,***
******.***.gy Guyana***,***
******************.***.uk GB***,***
*******.it Germany*,***,***
*********.org United States*,***,***
*******************.de Sweden*,***,***
*********.ch Switzerland*,***,***
*****.it Italy*,***,***
*****************.org Germany*,***,***
********.ch Switzerland*,***,***
See full domain list

FAQ

CVE-2026-8840 is Missing Authorization in Booking Calendar
A total of 655 websites have been identified as vulnerable to CVE-2026-8840, based on global website indexing conducted by WebTechSurvey.
The Booking Calendar is affected by the CVE-2026-8840 vulnerability.
Booking Calendar versions up to and including 3.2.36 are vulnerable to CVE-2026-8840.

References