CVE-2025-57923 is a vulnerability categorized under CWE-201 (Insertion of Sensitive Information Into Sent Data) affecting the Ideal Postcodes UK Address Postcode Validation WordPress plugin, versions up to 3.9.2. The flaw stems from the plugin exposing the API key in transmitted data when the API key is created with default settings that leave the “Allowed URLs” field empty, effectively allowing the API key to be used from any domain. This exposure enables unauthorized third parties to retrieve the API key without authentication or user interaction, then reuse it across any domain. Since the API keys are unrestricted by default, attackers can exploit this to consume API credits illicitly, potentially leading to service disruption or financial loss for the legitimate key owner. The vulnerability is remotely exploitable over the network with low attack complexity and no privileges required. While the vulnerability does not directly impact data integrity or availability, the confidentiality breach of the API key can have downstream effects, including unauthorized data queries or service misuse. No patches are currently linked, so mitigation relies on configuration changes and monitoring. The vulnerability was published on September 22, 2025, with a CVSS v3.1 base score of 5.3, reflecting a medium severity level primarily due to confidentiality impact and ease of exploitation.

For European organizations, especially those operating websites or services that use the Ideal Postcodes UK Address Postcode Validation plugin, this vulnerability can lead to unauthorized disclosure and misuse of API keys. This misuse can result in depletion of API credits, causing service interruptions or unexpected costs. Organizations relying on postcode validation for customer address verification, shipping, or compliance may experience operational disruptions if API access is exhausted. Additionally, unauthorized use of API keys could expose organizations to reputational damage or regulatory scrutiny under data protection laws if the misuse leads to further data exposure. Since the vulnerability affects confidentiality but not integrity or availability, the primary impact is financial and operational rather than direct data corruption or downtime. The risk is heightened for organizations with default API key configurations and those lacking monitoring of API usage patterns.

Organizations should immediately audit their use of the Ideal Postcodes UK Address Postcode Validation plugin and verify API key configurations. Specifically, they must restrict the “Allowed URLs” field to only trusted domains to prevent unauthorized reuse of API keys. If possible, rotate existing API keys to invalidate any potentially exposed keys. Implement monitoring and alerting on API usage to detect unusual or excessive consumption that could indicate abuse. Consider applying web application firewall (WAF) rules to limit access to API endpoints. Additionally, keep the plugin updated and monitor vendor communications for patches or security advisories. For long-term security, adopt the principle of least privilege by creating API keys with minimal permissions and domain restrictions. Educate development and operations teams about secure API key management practices to prevent similar issues.