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Researchers at cybersecurity firm Qualys have identified a potentially serious vulnerability in OpenSMTPD that can allow remote command execution with elevated privileges.

OpenSMTPD is the OpenBSD Project’s free and open source implementation of the Simple Mail Transfer Protocol (SMTP). The portable version of OpenSMTPD can run on various BSD and Linux distributions, as well as Apple’s Mac OS X operating system.

According to Qualys, OpenSMTPD is affected by a vulnerability that can allow an attacker to execute arbitrary shell commands with root privileges. The flaw can be exploited locally in OpenSMTPD’s default configuration, and both locally and remotely in the case of OpenSMTPD’s "uncommented" default configuration.

The vulnerability, tracked as CVE-2020-7247, exists in the smtp_mailaddr() function, which is responsible for validating sender and recipient email addresses. Attacks can be carried out via specially crafted emails.

In its advisory for CVE-2020-7247, Qualys says the flaw has been exploitable since May 2018. The company has shared technical details and there is a discussion on Hacker News about the vulnerability and its root cause.