CVE-2025-4295 is a medium severity vulnerability identified in the HotelRunner B2B platform, specifically affecting versions prior to 04.06.2025. The root cause of this vulnerability is improper validation of certificates when there is a host mismatch (CWE-297). This means that the system does not correctly verify that the SSL/TLS certificate presented by a server matches the expected hostname, potentially allowing attackers to exploit this weakness. The improper validation can lead to HTTP Response Splitting attacks, where an attacker manipulates HTTP headers to inject malicious responses or split the response stream. This can result in cache poisoning, cross-site scripting (XSS), or web cache deception attacks. The CVSS v3.1 base score is 4.6, indicating a medium severity level, with the vector showing network attack vector (AV:N), low attack complexity (AC:L), requiring low privileges (PR:L), and user interaction (UI:R). The impact affects confidentiality and integrity but not availability. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability is significant because HotelRunner B2B is a platform used by businesses in the hospitality sector to manage bookings and related services, making it a valuable target for attackers aiming to intercept or manipulate sensitive business communications or customer data.

For European organizations, especially those in the hospitality and travel sectors using HotelRunner B2B, this vulnerability could lead to unauthorized interception or manipulation of business communications. Attackers exploiting this flaw could perform HTTP Response Splitting to inject malicious content, potentially leading to session hijacking, phishing, or data leakage. This undermines trust in the platform and could result in reputational damage, regulatory penalties under GDPR for data breaches, and financial losses. Since the vulnerability affects confidentiality and integrity but not availability, the primary risks involve data exposure and manipulation rather than service disruption. The requirement for low privileges and user interaction means that attackers might need to trick users into performing actions, but the network attack vector allows exploitation remotely, increasing the threat surface. Given the interconnected nature of hospitality services across Europe, a successful exploit could cascade, affecting multiple partners and customers.

European organizations using HotelRunner B2B should immediately verify their software version and plan to upgrade to version 04.06.2025 or later once available. Until a patch is released, organizations should implement strict network-level controls such as web application firewalls (WAFs) configured to detect and block HTTP Response Splitting attempts. Additionally, enforcing strict TLS certificate validation policies on client and server sides can help mitigate the risk. Organizations should educate users about phishing and suspicious link interactions to reduce the risk of user interaction exploitation. Monitoring HTTP headers and logs for anomalies indicative of response splitting or injection attempts is recommended. Finally, engaging with HotelRunner support for any interim fixes or workarounds and maintaining up-to-date threat intelligence feeds will help in proactive defense.