Attack Chain

1. Attacker identifies a vulnerable system running a Microsoft product using the affected net-imap component.
2. Attacker crafts a malicious IMAP command containing a command injection payload within the “raw” argument.
3. Attacker sends the crafted IMAP command to the vulnerable server.
4. The net-imap component processes the command, improperly sanitizing the “raw” argument.
5. The injected command is executed by the server’s operating system with the privileges of the IMAP service.
6. Attacker gains arbitrary code execution on the server.
7. Attacker may install malware, steal sensitive data, or pivot to other systems within the network.

Impact

Successful exploitation of CVE-2026-42257 allows an attacker to execute arbitrary commands on the compromised system. This can lead to complete system compromise, data theft, and disruption of services. The specific impact depends on the privileges of the IMAP service account, but could potentially allow an attacker to gain full control over the server. Given the widespread use of IMAP for email communication, this vulnerability poses a significant risk to organizations.

Recommendation

• Apply the security update provided by Microsoft to patch CVE-2026-42257 on systems using the affected net-imap component.
• Deploy the Sigma rule “Detect CVE-2026-42257 Exploitation via Malicious IMAP Command” to detect exploitation attempts.
• Monitor network traffic for suspicious IMAP commands containing shell metacharacters.
• Review and harden the configuration of IMAP services to limit the impact of potential command injection vulnerabilities.