Critical Exim Mail Server Vulnerability Exposes Millions to Malicious Attachments

A critical security issue has been disclosed in the Exim mail transfer agent that could empower menace actors to supply destructive attachments to goal users’ inboxes.

The vulnerability, tracked as CVE-2024-39929, has a CVSS rating of 9.1 out of 10.. It has been resolved in variation 4.98.

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“Exim as a result of 4.97.1 misparses a multiline RFC 2231 header filename, and therefore distant attackers can bypass a $mime_filename extension-blocking safety mechanism, and probably produce executable attachments to the mailboxes of close people,” according to a description shared on the U.S. Nationwide Vulnerability Database (NVD).

Exim is a free of charge, mail transfer agent that’s used in hosts that are running Unix or Unix-like working systems. It was initial released in 1995 for use at the University of Cambridge.

Attack floor management firm Censys stated 4,830,719 of the 6,540,044 public-facing SMTP mail servers are managing Exim. As of July 12, 2024, 1,563,085 internet-accessible Exim servers are jogging a likely susceptible model (4.97.1 or earlier).

A bulk of the vulnerable cases are positioned in the U.S., Russia, and Canada.

“The vulnerability could allow a distant attacker to bypass filename extension blocking protection measures and provide executable attachments immediately to end-users’ mailboxes,” it pointed out. “If a person have been to obtain or run 1 of these malicious documents, the process could be compromised.”

This also implies that prospective targets need to click on on an attached executable for the attack to be productive. Though there are no stories of energetic exploitation of the flaw, it truly is crucial that end users move speedily to implement the patches to mitigate prospective threats.

The development arrives nearly a year soon after the project maintainers a established of six vulnerabilities in Exim that could end result in info disclosure and distant code execution.

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