CVE-2025-5256 is an Open Redirection vulnerability identified in Mautic, a popular open-source marketing automation platform widely used for managing email campaigns, customer engagement, and lead generation. The vulnerability exists specifically in the user unlocking endpoint (/s/action/unlock/user.user/0), where the returnUrl parameter is used to redirect users after completing an action. Due to insufficient validation or sanitization of this parameter, an attacker can craft malicious URLs that redirect users to arbitrary external websites controlled by the attacker. This flaw enables attackers to conduct phishing attacks by luring legitimate users into clicking on seemingly trustworthy links that ultimately lead to malicious sites. These malicious sites could host exploit kits or other malware delivery mechanisms, potentially compromising user credentials or systems. The vulnerability affects all Mautic versions greater than 1.0.0, indicating a broad impact across many deployments. The CVSS v3.1 base score is 5.4 (medium severity), reflecting that the attack vector is network-based, requires no privileges, but does require user interaction (clicking the malicious link). The impact on confidentiality and integrity is low, with no direct impact on availability. There are no known exploits in the wild at the time of publication. The recommended mitigation is to update Mautic to a version that properly validates or sanitizes the returnUrl parameter, ensuring redirects only occur to trusted internal URLs or explicitly whitelisted domains, thereby preventing abuse of this redirection mechanism.

For European organizations using Mautic, this vulnerability poses a significant risk primarily in the form of phishing attacks and social engineering campaigns. Attackers can exploit the open redirect to craft convincing emails or messages that appear to originate from legitimate marketing campaigns or internal communications, increasing the likelihood of user clicks. This can lead to credential theft, unauthorized access, or malware infections, which in turn can compromise sensitive customer data or internal systems. Given the GDPR regulatory environment in Europe, any data breach resulting from such attacks could lead to substantial fines and reputational damage. Marketing teams and customer engagement platforms are often integrated with CRM and sales systems, so a successful attack could also impact business operations and customer trust. While the vulnerability does not directly compromise system availability or integrity, the indirect effects through phishing and malware delivery can be severe. Organizations with large customer bases or those in sectors such as finance, healthcare, and retail—where trust and data protection are paramount—are particularly at risk.

1. Immediate update of Mautic installations to the latest patched version that includes proper validation or sanitization of the returnUrl parameter. 2. Implement strict URL validation rules within Mautic configurations or web application firewalls (WAFs) to allow redirects only to internal or explicitly whitelisted domains. 3. Conduct regular security awareness training for marketing and IT teams to recognize and report suspicious URLs and phishing attempts. 4. Monitor outbound links in marketing campaigns for unexpected redirects or anomalies. 5. Employ email security solutions with URL rewriting and scanning capabilities to detect and block malicious redirects before reaching end users. 6. Review and restrict permissions for users who can configure URLs and redirects within Mautic to minimize the risk of insider misuse. 7. Establish incident response procedures to quickly address phishing incidents potentially leveraging this vulnerability. These steps go beyond generic advice by focusing on configuration hardening, user training, and proactive monitoring tailored to the marketing automation context.