CVE-2025-40630 is an open redirection vulnerability (CWE-601) identified in IceWarp Mail Server version 11.4.0. This vulnerability allows an attacker to craft malicious URLs that, when clicked by a user, redirect the user to an arbitrary external domain controlled by the attacker. The issue arises due to improper validation or sanitization of URL parameters or path segments, enabling attackers to manipulate the redirection logic. For example, URLs such as “https://icewarp.domain.com//<MALICIOUS_DOMAIN>/%2e%2e” exploit path traversal encoding to bypass restrictions and redirect users to untrusted sites. The vulnerability has been confirmed to be exploitable in Firefox browsers. The CVSS 4.0 base score is 5.1 (medium severity), reflecting that the attack vector is network-based, requires no privileges, but does require user interaction (clicking the malicious link). The vulnerability does not impact confidentiality, integrity, or availability directly but can be leveraged in phishing campaigns or social engineering attacks to trick users into visiting malicious sites, potentially leading to credential theft, malware installation, or further exploitation. No known exploits are currently in the wild, and no patches have been linked yet, indicating that organizations should monitor for vendor updates. The vulnerability was reserved in April 2025 and published in May 2025, with INCIBE as the assigner.

For European organizations using IceWarp Mail Server 11.4.0, this vulnerability poses a significant risk primarily in the context of phishing and social engineering attacks. Attackers can exploit the open redirect to craft convincing URLs that appear to originate from a trusted corporate mail server domain, increasing the likelihood that users will click on malicious links. This can lead to users being redirected to credential harvesting sites, malware distribution points, or other malicious destinations. While the vulnerability itself does not allow direct compromise of the mail server or data leakage, it undermines user trust and can serve as a stepping stone for more severe attacks. Organizations with large user bases or those in regulated sectors (finance, healthcare, government) may face reputational damage or compliance issues if users fall victim to attacks leveraging this vulnerability. Additionally, since the vulnerability requires no authentication and can be exploited remotely, it increases the attack surface for threat actors targeting European enterprises relying on IceWarp mail infrastructure.

1. Immediate mitigation should include educating users about the risks of clicking on unexpected or suspicious links, especially those purporting to come from internal mail servers. 2. Network-level controls such as web proxies or URL filtering solutions should be configured to detect and block suspicious redirection patterns originating from the IceWarp domain. 3. Administrators should monitor web server logs for unusual URL patterns indicative of exploitation attempts. 4. Implement Content Security Policy (CSP) headers and other browser security mechanisms to limit the impact of redirection-based attacks. 5. IceWarp administrators should isolate the mail server from direct internet exposure where possible, using reverse proxies or gateways that can perform input validation and sanitization. 6. Organizations should track vendor advisories closely and apply patches or updates as soon as they become available. 7. Consider deploying multi-factor authentication (MFA) to reduce the impact of credential theft resulting from phishing attacks leveraging this vulnerability. 8. Review and harden URL handling logic in custom integrations or plugins that interact with IceWarp Mail Server to prevent similar issues.