UNC1151 exploiting Roundcube to steal user credentials in a spearphishing campaign

The UNC1151 threat actor is conducting a spearphishing campaign exploiting a critical vulnerability (CVE-2024-42009) in the Roundcube webmail client. Malicious JavaScript embedded in phishing emails installs a stealthy Service Worker in victims' browsers upon opening the email, intercepting login credentials and exfiltrating them without further user interaction. A second vulnerability (CVE-2025-49113) may be chained to increase persistence and impact. Stolen credentials enable attackers to access mailboxes, harvest address books, and propagate phishing internally, facilitating lateral movement. The campaign primarily targets Polish organizations but also threatens neighboring Central European countries with significant Roundcube deployments. Organizations are urged to patch vulnerabilities, monitor for unusual Service Worker activity, enforce multi-factor authentication, and enhance email filtering to mitigate risks.

• CVE-2024-42009: RoundCube Webmail Cross-Site Scripting VulnerabilityCriticalVulnerability2025-06-09
• CVE-2025-49113: Roundcube Webmail · Deserialization of Untrusted DataCriticalVulnerability2025-06-02
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