CVE-2021-3901 in Firefly III
Summary
by MITRE • 10/28/2021
firefly-iii is vulnerable to Cross-Site Request Forgery (CSRF)
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Analysis
by VulDB Data Team • 11/01/2021
The firefly-iii web application presents a critical cross-site request forgery vulnerability that compromises the integrity of user sessions and potentially enables unauthorized actions within the application. This vulnerability exists due to insufficient validation of request origins and lack of proper anti-CSRF token implementation in the application's authentication and transaction processing flows. The flaw allows attackers to trick authenticated users into executing unintended actions such as transferring funds, modifying account settings, or creating malicious transactions without their knowledge or consent.
This vulnerability maps directly to CWE-352, which specifically addresses Cross-Site Request Forgery weaknesses in web applications. The technical implementation flaw stems from the application's failure to properly validate the referer header or implement robust anti-CSRF tokens in critical endpoints. The attack surface includes all authenticated functions within firefly-iii that process financial transactions, account modifications, and user preference changes. Without proper origin validation or token verification, malicious actors can craft specially crafted requests that appear legitimate to the application's security mechanisms.
The operational impact of this vulnerability extends beyond simple data theft or modification. An attacker could potentially drain user accounts, create fraudulent transactions, alter financial reporting, or manipulate user access controls. The consequences are particularly severe for financial applications like firefly-iii where users store sensitive banking and budgeting information. The vulnerability affects the application's confidentiality, integrity, and availability by enabling unauthorized modifications to user data and potentially disrupting normal application operations.
Mitigation strategies should include immediate implementation of anti-CSRF tokens for all state-changing requests, proper validation of HTTP referer headers, and enforcement of origin checking mechanisms. The application should generate unique tokens for each user session and validate these tokens on every critical request. Additionally, implementing the SameSite cookie attributes and proper Content Security Policy headers would provide additional layers of protection. Organizations should also consider implementing rate limiting and transaction confirmation mechanisms for high-risk operations. This vulnerability aligns with ATT&CK technique T1531 which focuses on establishing persistence through manipulation of authentication mechanisms, and T1078 which addresses legitimate credentials usage for unauthorized access.
The remediation process requires comprehensive code review of all endpoints handling user transactions and account modifications. Security patches should be deployed immediately to ensure all authenticated requests require proper token validation. Regular security testing including penetration testing and automated vulnerability scanning should be implemented to identify similar issues in other application components. The fix must also consider the application's architecture to ensure that CSRF protection is consistently applied across all modules and that user sessions maintain proper state validation throughout their lifecycle.