CVE-2025-4296 is an Open Redirect vulnerability (CWE-601) identified in the HotelRunner B2B platform, specifically affecting versions prior to 04.06.2025. This vulnerability allows attackers to craft URLs that redirect users to untrusted external sites without proper validation. The flaw enables forceful browsing, where an attacker can manipulate URL parameters to redirect victims to malicious websites, potentially facilitating phishing attacks, credential theft, or distribution of malware. The vulnerability has a CVSS 3.1 base score of 4.7, indicating a medium severity level. The vector metrics indicate that the attack can be executed remotely (AV:N), requires low attack complexity (AC:L), no privileges (PR:N), but does require user interaction (UI:R). The scope is changed (S:C), meaning the vulnerability affects resources beyond the initially vulnerable component. The impact affects integrity (I:L) but not confidentiality or availability. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability arises from insufficient validation of redirect URLs, allowing attackers to bypass intended navigation flows and redirect users to potentially harmful external sites. This can undermine user trust and lead to secondary attacks such as credential harvesting or malware infection.

For European organizations using HotelRunner B2B, this vulnerability poses a risk primarily to the integrity of user navigation and trust. Attackers could exploit the open redirect to lure employees, partners, or customers to malicious sites, increasing the risk of phishing and social engineering attacks. This could lead to credential compromise or unauthorized access to corporate resources. While the vulnerability does not directly impact confidentiality or availability, the secondary effects of successful phishing or malware delivery could have significant operational and reputational consequences. Given the B2B nature of the product, business partners and clients across Europe could be targeted, potentially impacting supply chain security and business continuity. Organizations in sectors with high reliance on online booking and travel management, such as hospitality, travel agencies, and corporate travel departments, may face elevated risks.

To mitigate this vulnerability, European organizations should first verify if they are running affected versions of HotelRunner B2B and prioritize upgrading to the fixed version once available. In the interim, organizations can implement strict URL validation and filtering on their web gateways or reverse proxies to detect and block suspicious redirect URLs. Security teams should monitor web traffic for unusual redirect patterns and educate users about the risks of clicking on unexpected links, especially those originating from the HotelRunner B2B platform. Implementing web application firewalls (WAFs) with custom rules to detect open redirect attempts can provide an additional layer of defense. Furthermore, organizations should review and tighten their internal policies on URL redirection and consider multi-factor authentication to reduce the impact of potential credential theft resulting from phishing attacks leveraging this vulnerability.