CISA Catalogs Critical Roundcube Deserialization Vulnerability Under Active Exploitation

Vulnerability Overview

The Cybersecurity and Infrastructure Security Agency (CISA) has updated its Known Exploited Vulnerabilities (KEV) catalog to include two security flaws impacting Roundcube webmail software. The most significant of these is CVE-2025-49113, which carries a CVSS score of 9.9. This vulnerability involves the deserialization of untrusted data, providing a path for unauthenticated remote code execution (RCE) on affected mail servers.

Technical Analysis: CVE-2025-49113

The defect resides in how Roundcube processes serialized objects within its webmail interface. Inadequate input validation allows an attacker to submit malicious serialized payloads that, upon reconstruction by the server’s backend, trigger unintended code execution.

• Vulnerability Type: CWE-502 (Deserialization of Untrusted Data).
• Attack Vector: Network/Remote.
• Authentication Requirement: None.
• Impact: Complete system compromise, unauthorized data access, and potential lateral movement within the network.

Threat Actor Context and TTPs

Active exploitation has been observed in the wild, suggesting that threat actors are targeting webmail infrastructure to gain initial access to organizational environments. Historical exploitation of Roundcube vulnerabilities has frequently been associated with state-sponsored advanced persistent threats (APTs) aiming to intercept sensitive communications. The TTPs (Tactics, Techniques, and Procedures) typically involve the delivery of crafted HTTP requests to vulnerable endpoints to establish a persistent foothold.

Remediation and Mitigation

Under Binding Operational Directive (BOD) 22-01, Federal Civilian Executive Branch (FCEB) agencies are required to remediate these vulnerabilities within a specified timeframe.

1. Immediate Update: Administrators must update Roundcube instances to the latest stable version that specifically addresses CVE-2025-49113.
2. Input Filtering: Implement strict web application firewall (WAF) rules to detect and block suspicious serialized patterns in incoming traffic.
3. Audit Logs: Monitor web server and application logs for anomalous process spawning or unauthorized access to sensitive directories.
4. Least Privilege: Ensure the web server user (e.g., www-data or apache) has minimal permissions to limit the blast radius of an RCE event.