CVE-2025-4035 is a vulnerability discovered in the libsoup HTTP client library, which is part of Red Hat Enterprise Linux 10. The issue arises from libsoup's incorrect handling of case sensitivity when processing cookies for public suffix domains. Specifically, when a domain contains at least two components and includes uppercase characters, libsoup clients mistakenly allow cookies to be set for these public suffix domains. Public suffix domains are meant to be protected to prevent cookies from being set across unrelated domains, which is a critical security control to prevent cookie-based attacks such as session fixation or cross-site request forgery. By bypassing this protection, a malicious website can set cookies for domains it does not own, potentially leading to integrity violations like session fixation where an attacker can hijack or manipulate user sessions. The vulnerability is exploitable remotely without any privileges but requires user interaction, such as visiting a malicious website. The CVSS 3.1 score is 4.3 (medium severity), reflecting the limited impact on confidentiality and availability but a notable impact on integrity. No known exploits have been reported in the wild, and no patches or mitigations have been linked yet. This vulnerability affects applications relying on libsoup for HTTP client functionality within Red Hat Enterprise Linux 10 environments.

For European organizations, this vulnerability could lead to session fixation attacks, allowing attackers to hijack user sessions or manipulate session data, potentially compromising the integrity of web applications and services. While confidentiality and availability impacts are minimal, the integrity breach can facilitate further attacks such as privilege escalation or unauthorized actions within applications. Organizations using Red Hat Enterprise Linux 10, especially those running web services or applications that utilize libsoup for HTTP communications, are at risk. This includes sectors like finance, government, healthcare, and critical infrastructure where session integrity is paramount. The requirement for user interaction means phishing or social engineering could be used to exploit this vulnerability. The lack of known exploits currently reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits once patches are released. Failure to address this vulnerability could lead to targeted attacks against European entities relying on affected systems.

Organizations should monitor Red Hat advisories closely for patches addressing CVE-2025-4035 and apply them promptly once available. In the interim, consider implementing strict cookie policies at the application level to reject cookies set for public suffix domains, especially those containing uppercase characters. Web application firewalls (WAFs) can be configured to detect and block suspicious cookie-setting behaviors. Educate users to avoid visiting untrusted or suspicious websites to reduce the risk of exploitation via user interaction. Security teams should audit applications using libsoup to identify exposure and consider alternative HTTP client libraries if feasible. Additionally, enable and enforce secure cookie attributes such as HttpOnly and Secure flags to limit cookie misuse. Regularly review session management practices to detect anomalies indicative of session fixation or hijacking attempts.