thimpress WP Hotel Booking Plugin up to 2.3.1 on WordPress IPN web_hook_process_paypal_standard test_ipn authentication replay

Summaryinfo

A vulnerability categorized as critical has been discovered in thimpress WP Hotel Booking Plugin up to 2.3.1. Impacted is the function web_hook_process_paypal_standard of the component IPN Handler. Such manipulation of the argument test_ipn leads to authentication replay. This vulnerability is documented as CVE-2026-11901. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in thimpress WP Hotel Booking Plugin up to 2.3.1. It has been rated as critical. Affected by this issue is the function web_hook_process_paypal_standard of the component IPN Handler. The manipulation of the argument test_ipn with an unknown input leads to a authentication replay vulnerability. Using CWE to declare the problem leads to CWE-294. A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes). Impacted is confidentiality, integrity, and availability. CVE summarizes:

The WP Hotel Booking plugin for WordPress is vulnerable to Insufficient Verification of Data Authenticity in all versions up to, and including, 2.3.1. This is due to the `web_hook_process_paypal_standard()` IPN handler selecting its PayPal validation endpoint from the attacker-controlled `$_REQUEST['test_ipn']` parameter, force-upgrading any `pending` transaction to `completed` when `test_ipn=1`, and omitting post-verification checks on `receiver_email`, `mc_currency`, and `txn_id` uniqueness after receiving a `VERIFIED` response from PayPal. This makes it possible for unauthenticated attackers to mark arbitrary hotel bookings as fully paid without submitting genuine payment to the merchant — either by routing IPN validation through PayPal's sandbox using a free sandbox account, or by replaying a previously verified IPN from a nominal payment to an attacker-controlled PayPal account. An attacker requires only a free PayPal sandbox account (or any PayPal account) to obtain a `VERIFIED` response; no site credentials or special configuration are needed.

The advisory is shared for download at wordfence.com. This vulnerability is handled as CVE-2026-11901 since 06/10/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 07/11/2026). The MITRE ATT&CK project declares the attack technique as T1040.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• WordPress Plugin

Vendor

• thimpress

Name

• WP Hotel Booking Plugin

Version

• 2.3.0
• 2.3.1

CPE 2.3info

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CPE 2.2info

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Once again VulDB remains the best source for vulnerability data.

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