Exim Internet Mailer Found Vulnerable to RCE And DoS Bugs; Patch Now

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by Mohit Kumar

November 26, 2017

A security researcher has discovered and publicly disclosed two critical vulnerabilities in the popular Internet mail message transfer agent Exim, one of which could allow a remote attacker to execute malicious code on the targeted server.

Exim is an open source mail transfer agent (MTA) developed for Unix-like operating systems such as Linux, Mac OSX or Solaris, which is responsible for routing, delivering and receiving email messages.

The first vulnerability, identified as CVE-2017-16943, is a use-after-free bug which could be exploited to remotely execute arbitrary code in the SMTP server by crafting a sequence of BDAT commands.

“To trigger this bug, BDAT command is necessary to perform an allocation by raising an error,” the researcher said. “Through our research, we confirm that this vulnerability can be exploited to remote code execution if the binary is not compiled with PIE.”

The researcher (mehqq_) has also published a Proof-of-Concept (PoC) exploit code written in python that could allow anyone to gain code execution on vulnerable Exim servers.

The second vulnerability, identified as CVE-2017-16944, is a denial of service (DoS) flaw that could allow a remote attacker to hang Exim servers even the connection is closed by forcing it to run in an infinite loop without crashing.

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