CVE-2026-27584 is a critical security vulnerability identified in the ActualBudget personal finance tool, specifically affecting versions prior to 26.2.1. The root cause is the absence of authentication middleware on the ActualBudget server component, which manages integration endpoints for SimpleFIN and Pluggy.ai. These endpoints provide access to sensitive financial data, including bank account balances and transaction histories. Because authentication is missing, any unauthenticated user with network access to the ActualBudget Server can query these endpoints and retrieve confidential user financial information. The vulnerability is classified under CWE-306 (Missing Authentication for Critical Function), indicating a failure to enforce access controls on sensitive operations. The CVSS 4.0 base score is 9.2, reflecting a network attack vector (AV:N), no required privileges (PR:N), no user interaction (UI:N), and a high impact on confidentiality (VC:H) without affecting integrity or availability. The vulnerability affects all ActualBudget Server deployments that have SimpleFIN or Pluggy.ai integrations enabled and are reachable over the network. The vendor has addressed this issue in version 26.2.1 by introducing proper authentication middleware to protect these endpoints. No known exploits are currently reported in the wild, but the ease of exploitation and severity make this a critical risk for affected users.

The primary impact of CVE-2026-27584 is the unauthorized disclosure of sensitive financial information, including bank account balances and transaction histories of ActualBudget users. This breach of confidentiality can lead to financial fraud, identity theft, and privacy violations. Organizations relying on ActualBudget Server with SimpleFIN or Pluggy.ai integrations are at risk of data leakage if their server instances are exposed to untrusted networks. Since no authentication or user interaction is required, attackers can easily automate data harvesting attacks. The vulnerability does not affect data integrity or availability directly but severely compromises user trust and regulatory compliance, especially under data protection laws such as GDPR or CCPA. Financial institutions, fintech companies, and personal finance users leveraging ActualBudget could face reputational damage and legal consequences if exploited. The scope is limited to ActualBudget Server deployments with these integrations enabled and network exposure, but given the sensitivity of the data, the impact is critical.

To mitigate CVE-2026-27584, organizations should immediately upgrade ActualBudget Server to version 26.2.1 or later, which includes the necessary authentication middleware to secure the SimpleFIN and Pluggy.ai endpoints. Until the upgrade is applied, administrators should restrict network access to the ActualBudget Server instances by implementing firewall rules or network segmentation to limit exposure to trusted internal networks only. Disable or remove SimpleFIN and Pluggy.ai integrations if they are not essential, reducing the attack surface. Conduct thorough audits of server logs to detect any unauthorized access attempts to these endpoints. Employ network monitoring tools to identify anomalous queries targeting the integration endpoints. Additionally, enforce strong access controls and consider deploying Web Application Firewalls (WAFs) to block unauthorized requests. Educate users about the importance of timely software updates and monitor vendor advisories for any further patches or mitigations.