CVE-2025-63828 is a Host Header Injection vulnerability identified in Backdrop CMS version 1.32.1. The flaw arises because the application fails to properly validate the Host header in HTTP requests, specifically during password reset operations. An attacker can craft a malicious request with a manipulated Host header, causing the application to generate password reset links that redirect users to attacker-controlled domains. This redirection can be exploited to perform phishing attacks or to inject malicious cookies, leading to session hijacking. The vulnerability impacts the confidentiality and integrity of user sessions by allowing attackers to impersonate legitimate users or capture sensitive authentication tokens. Although no CVSS score has been assigned yet, the vulnerability is significant due to the ease of exploitation (no authentication required), the potential for widespread impact on user accounts, and the critical nature of password reset functionality. No known exploits are currently reported in the wild, but the vulnerability is publicly disclosed and should be addressed promptly. The lack of patch links indicates that a fix may not yet be available, emphasizing the need for interim mitigations such as input validation and web application firewall rules.

For European organizations, this vulnerability poses a serious risk to user account security and trust. Attackers exploiting this flaw can redirect users to malicious websites, facilitating phishing campaigns and credential theft. Session hijacking through cookie injection can lead to unauthorized access to sensitive systems and data, potentially resulting in data breaches and compliance violations under GDPR. Organizations relying on Backdrop CMS for public-facing websites, especially those offering password reset features, are vulnerable to account takeover attacks. The impact extends to reputational damage, financial loss, and regulatory penalties. Given the widespread use of CMS platforms in Europe, particularly in Germany, France, and the UK, the threat could affect a broad range of sectors including government, finance, healthcare, and e-commerce. The absence of a patch increases the urgency for organizations to implement compensating controls to mitigate risk.

1. Immediately implement strict validation and sanitization of the Host header in all HTTP requests, ensuring only expected and trusted hostnames are accepted. 2. Configure web application firewalls (WAFs) to detect and block requests with suspicious or unexpected Host headers, particularly those targeting password reset endpoints. 3. Monitor password reset workflows for unusual redirect patterns or spikes in reset requests that may indicate exploitation attempts. 4. Educate users to recognize phishing attempts that may arise from malicious redirects linked to this vulnerability. 5. Regularly audit and update Backdrop CMS installations and monitor vendor communications for official patches or security updates addressing this issue. 6. Consider implementing multi-factor authentication (MFA) to reduce the impact of compromised credentials. 7. Review and tighten cookie security settings, such as setting the HttpOnly and Secure flags, to mitigate cookie injection risks. 8. If feasible, temporarily disable password reset functionality or restrict it to verified users until a patch is available.