Linux worm spreading via Exim servers hit Azure customers
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2019-10149 | Unvalidated Email Recipient Enables Remote Command Execution in Exim MTA CVE-2019-10149 is an improper input validation flaw (CWE-78, OS command injection) in the deliver_message() function in /src/deliver.c of the Exim mail transfer agent, where email recipient addresses are not safely validated before use. A remote attacker triggers it by sending mail whose recipient address contains crafted Exim string-expansion syntax (such as ${run{...}}), causing Exim to expand and execute attacker-supplied operating-system commands during recipient verification or delivery. An attacker gains arbitrary remote command execution on the mail server, commonly with elevated privileges, enabling full system compromise, data theft, ransomware deployment (e.g., the Trinity ransomware campaign), or installation of botnet implants. Any organization running an internet-exposed Exim MTA in the affected version range is at risk, and Exim is widely deployed as the default mail server on many Linux distributions. Exploitation is confirmed in the wild: mass scanning and compromise campaigns began shortly after the June 2019 disclosure, CISA added the flaw to its Known Exploited Vulnerabilities catalog on 2022-01-10, and its EPSS score of 100% (100th percentile) reflects near-certain near-term exploitation risk. Do: Upgrade Exim to 4.92 or later, or install your distribution's patched Exim package, as required by CISA's KEV action ('apply updates per vendor instructions'); if patching must be delayed, restrict internet-facing SMTP access and tighten recipient-verification configuration. Check mail logs for suspicious MAIL FROM/RCPT TO addresses containing expansion syntax such as ${run{...}} or shell-like commands, and audit patched servers for post-compromise artifacts such as unusual cron jobs, downloaded binaries, or new authorized SSH keys. | 9.8 | 100% | KEV PoC ×5 |
| mass≈500,000+ internet-exposed Exim SMTP servers, with hundreds of thousands likely running vulnerable versions |
Full article587 words · extracted from securityaffairs.com · click to collapse
On Friday, security experts at Microsoft warned of a new Linux worm, spreading via Exim email servers, that already compromised some Azure installs.
Bad actors continue to target cloud services in the attempt of abusing them for several malicious purposes, like storing malware or implementing command and control servers.
Microsoft Azure is not immune, recently experts reported several attacks leveraging the platform to host tech-support scam and phishing templates.
Researchers already warned of the presence of some malware on the Microsoft Azure platform.
https://twitter.com/JayTHL/status/1127334608142503936
At the end of last week, Microsoft warned of a new Linux worm, spreading via Exim servers, that already compromised some Azure installs.
Recently security experts reported ongoing attacks targeting millions of mail servers running vulnerable Exim mail transfer agent (MTA) versions. Different groups of hackers are exploiting the CVE-2019-10149 flaw to take over them.
The critical vulnerability affects versions 4.87 to 4.91 of the Exim mail transfer agent (MTA) software. The flaw could be exploited by unauthenticated remote attackers to execute arbitrary commands on mail servers for some non-default server configurations.
The CVE-2019-10149 issue resides in the deliver_message() function in /src/deliver.c and it is caused by the improper validation of recipient addresses. The flaw could lead to remote code execution with root privileges on the mail server, unfortunately, the vulnerability is easily exploitable by a local and a remote attacker in certain non-default configurations
The CVE-2019-10149 flaw was addressed the Exim’s development team with the release of version 4.92 in February, but a large number of operating systems are still affected by the flaw.
“CVE-2019-10149, which was first discovered on June 5, is now being used as the vulnerability for a widespread campaign to attack exim servers and propagate across the Internet.” reads a blog post published by Cybereason.
“We are aware of an initial wave of attacks as described by Freddie Leeman on June 9, 2019. The first hacker group began pushing exploits from a C2 server located on the clear web. A second round of attacks by a different attacker are being analyzed by the Nocturnus team.”
Attackers are scanning the internet for vulnerable mail servers then when they will be compromised the initially deployed script will download a second script designed to check if OpenSSH is installed on the compromised machine.
In case OpenSSH is not present, it will install it and start it to gain root logins via SSH using a private/public RSA key for authentication.
Microsoft has now detected a Linux worm that leverages the above flaw in vulnerable Linux Exim email servers in a cryptojacking campaign.
“This week, MSRC confirmed the presence of an active Linux worm leveraging a critical Remote Code Execution (RCE) vulnerability, CVE-2019-10149, in Linux Exim email servers running Exim version 4.87 to 4.91. Azure customers running VMs with Exim 4.92 are not affected by this vulnerability.” reads the advisory published by Microsoft.
Microsoft pointed out that Azure has already implemented controls to limit the spread of this Linux worm, but warns customers of using up to date software to prevent the infection.
“Customers using Azure virtual machines (VMs) are responsible for updating the operating systems running on their VMs.” continues the advisory. “As this vulnerability is being actively exploited by worm activity, MSRC urges customers to observe Azure security best practices and patterns and to patch or restrict network access to VMs running the affected versions of Exim.”
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(SecurityAffairs – Exim, Linux worm)
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Text extracted automatically; images, tables and formatting may be missing. Original: https://securityaffairs.com/87168/hacking/linux-worm-exim-servers.html