CVE-2026-2153 identifies an open redirect vulnerability in the open-source authentication and access control tool 'doorman' developed by mwielgoszewski, affecting all versions up to 0.6. The vulnerability resides in the is_safe_url function within the doorman/users/views.py file, which is intended to validate URLs passed via the 'Next' parameter to prevent unsafe redirections. However, due to insufficient validation logic, an attacker can craft a URL with a manipulated 'Next' parameter that causes the application to redirect users to arbitrary external websites. This flaw can be exploited remotely without requiring authentication, but it necessitates user interaction, such as clicking a malicious link. The vulnerability's CVSS 4.0 score is 5.3, reflecting medium severity, primarily due to the lack of direct impact on confidentiality, integrity, or availability, but with a potential to facilitate social engineering attacks like phishing. Although no active exploits have been reported in the wild, the public disclosure of the vulnerability increases the likelihood of exploitation attempts. The open redirect can be leveraged by attackers to bypass security filters, steal user credentials, or distribute malware by redirecting users to malicious domains. The vulnerability affects all released versions from 0.1 through 0.6, and no official patches or fixes have been linked yet, requiring users to implement workarounds or code-level mitigations. Organizations relying on doorman for user authentication or session management should prioritize addressing this issue to prevent exploitation.

For European organizations, the open redirect vulnerability in doorman poses a moderate risk primarily through social engineering and phishing attacks. Attackers can exploit this flaw to redirect users to malicious websites that may host malware or credential harvesting pages, potentially compromising user accounts and organizational security. While the vulnerability does not directly compromise system confidentiality, integrity, or availability, it undermines user trust and can facilitate broader attacks such as session hijacking or unauthorized access if combined with other vulnerabilities. Organizations that integrate doorman into their authentication workflows or internal portals may see increased phishing risks targeting employees or customers. The impact is heightened in sectors with stringent regulatory requirements for data protection and user privacy, such as finance, healthcare, and government institutions across Europe. Additionally, the remote exploitability without authentication means attackers can target users en masse via phishing campaigns, increasing the threat surface. However, the requirement for user interaction limits automated exploitation, somewhat reducing the overall risk.

To mitigate CVE-2026-2153, European organizations using doorman should first check for any official patches or updates from the vendor and apply them promptly once available. In the absence of official fixes, developers should review and strengthen the is_safe_url function to ensure strict validation of the 'Next' parameter, allowing only internal or whitelisted URLs for redirection. Implementing a whitelist-based URL validation or using framework-provided safe redirect utilities is recommended. Additionally, organizations should implement security awareness training to educate users about the risks of clicking suspicious links, especially those involving redirects. Deploying web application firewalls (WAFs) with rules to detect and block suspicious redirect patterns can provide an additional layer of defense. Monitoring logs for unusual redirect requests and anomalous user behavior can help detect exploitation attempts early. Finally, consider adding multi-factor authentication (MFA) to reduce the impact of credential theft resulting from phishing attacks facilitated by this vulnerability.