CVE-2026-26747 in Monica
Summary
by MITRE • 02/20/2026
A Host Header Poisoning vulnerability exists in Monica 4.1.2 due to improper handling of the HTTP Host header in app/Providers/AppServiceProvider.php, combined with the default misconfiguration where the "app.force_url" is not set and default is "false". The application generates absolute URLs (such as those used in password reset emails) using the user-supplied Host header. This allows remote attackers to poison the password reset link sent to a victim,
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 02/27/2026
The vulnerability identified as CVE-2026-26747 represents a critical host header poisoning flaw within the Monica 4.1.2 application framework. This security weakness stems from inadequate validation and handling of the HTTP Host header within the application's service provider configuration file located at app/Providers/AppServiceProvider.php. The root cause of this vulnerability lies in the application's default configuration where the "app.force_url" parameter remains unset with a default value of "false", creating a dangerous operational environment where user-supplied host information can be directly incorporated into generated URLs without proper sanitization or validation.
The technical implementation of this vulnerability allows attackers to manipulate the HTTP Host header during request processing, enabling them to inject arbitrary host information into absolute URLs generated by the application. When the application constructs password reset links or other critical absolute URLs, it relies on the Host header value provided by the client rather than enforcing a trusted application domain. This behavior creates a pathway for attackers to craft malicious password reset emails containing links that redirect to attacker-controlled domains, effectively enabling credential theft and account takeover scenarios. The flaw operates at the application logic level where URL generation functions fail to properly validate or sanitize input from the HTTP Host header, directly violating secure coding principles for input validation and output encoding.
The operational impact of this vulnerability extends beyond simple password reset manipulation to encompass broader session management and authentication bypass capabilities. Attackers can leverage this weakness to redirect users to phishing domains when they click on password reset links, potentially harvesting credentials or personal information from unsuspecting victims. The vulnerability affects the application's trust model and undermines the security of user authentication flows, particularly targeting the password reset functionality which is a critical attack surface for credential compromise. This issue creates a persistent threat vector that can be exploited across multiple user interactions and session states, making it particularly dangerous for applications handling sensitive personal data or user accounts.
Mitigation strategies for this vulnerability require immediate configuration adjustments and code-level modifications to ensure proper host header validation and URL generation practices. The primary recommendation involves setting the "app.force_url" configuration parameter to a specific trusted domain value, preventing the application from accepting arbitrary host information from user requests. Additionally, developers should implement strict validation of Host header values within the AppServiceProvider.php file, ensuring that only authorized domains can be used for URL generation. This approach aligns with the principle of least privilege and input validation practices recommended in both CWE-645 and the OWASP Top Ten security guidelines. Security teams should also implement monitoring for unusual Host header patterns and consider implementing HTTP Strict Transport Security headers to further protect against header manipulation attacks. The vulnerability demonstrates the importance of proper configuration management and the critical need for applications to validate all user-supplied input before incorporating it into security-sensitive operations such as URL generation and authentication flows.