CVE-2025-3743 is a vulnerability identified in the Upsell Funnel Builder for WooCommerce plugin developed by wpswings, affecting all versions up to and including 3.0.0. This plugin is used within WordPress environments to create upsell funnels, which are marketing tools designed to increase sales by offering additional products or discounts during the checkout process. The vulnerability arises from improper handling of web parameters in the 'add_offer_in_cart' function. Specifically, the plugin allows unauthenticated attackers to externally manipulate parameters that were assumed to be immutable, namely the additional product ID and discount fields associated with order bumps. Because these parameters are not properly validated or protected, an attacker can arbitrarily change the product linked to any order bump and modify the discount applied to that item before it is added to the shopping cart. This flaw corresponds to CWE-472, which involves external control of assumed-immutable web parameters, leading to unauthorized modification of critical transaction data. The vulnerability does not require authentication or user interaction, making it accessible to any remote attacker who can send crafted requests to the affected WooCommerce site. Although no known exploits have been reported in the wild as of the publication date, the potential for abuse exists, especially in e-commerce environments where financial transactions are involved. The lack of a patch at the time of reporting further increases the risk for affected users. This vulnerability could be exploited to manipulate order details, potentially resulting in financial loss for merchants or disruption of sales processes.

For European organizations, especially those operating e-commerce platforms using WooCommerce with the Upsell Funnel Builder plugin, this vulnerability poses a significant risk. Attackers could exploit it to alter order details, such as substituting higher-priced products with lower-priced ones or applying unauthorized discounts, leading to direct financial losses. The integrity of sales data and revenue reporting could be compromised, affecting business operations and accounting accuracy. Additionally, repeated exploitation could damage customer trust if orders are incorrectly processed or if fraudulent discounts are applied. Given the plugin's role in the checkout process, availability could also be indirectly impacted if merchants disable the plugin or the entire WooCommerce system to mitigate risk, causing business disruption. The vulnerability's unauthenticated nature increases the attack surface, allowing widespread exploitation attempts. European organizations subject to strict data protection and financial regulations (e.g., GDPR, PCI DSS) may face compliance issues if such manipulations lead to data inaccuracies or financial discrepancies. The threat is particularly relevant for small to medium-sized enterprises (SMEs) that rely heavily on WooCommerce and may lack advanced security monitoring capabilities.

Immediately audit all WooCommerce installations to identify the use of the Upsell Funnel Builder plugin and verify the version in use. Temporarily disable the Upsell Funnel Builder plugin until a security patch or update is released by wpswings addressing CVE-2025-3743. Implement web application firewall (WAF) rules to detect and block suspicious requests attempting to manipulate 'add_offer_in_cart' parameters, focusing on anomalous changes to product IDs and discount values. Monitor e-commerce transaction logs for irregularities in order bumps, such as unexpected product substitutions or discount amounts inconsistent with marketing campaigns. Restrict direct access to the vulnerable function endpoints by enforcing IP whitelisting or rate limiting where feasible to reduce exposure to automated exploitation attempts. Engage with the plugin vendor for timely updates and subscribe to security advisories to apply patches promptly once available. Educate development and operations teams about the risks of external control of assumed-immutable parameters and encourage secure coding practices, including proper input validation and parameter integrity checks. Consider implementing additional server-side validation to cross-verify order bump details against expected values before processing transactions.