NSA warns Russia-linked APT group is exploiting Exim flaw since 2019
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 article531 words · extracted from securityaffairs.com · click to collapse
The U.S. NSA warns that Russia-linked APT group known as Sandworm Team have been exploiting a critical flaw in the Exim mail transfer agent (MTA).
The U.S. National Security Agency (NSA) is warning that Russia-linked APT group tracked Sandworm Team has been exploiting a critical vulnerability (CVE-2019-10149) in the Exim mail transfer agent (MTA) software since at least August 2019.
The CVE-2019-10149 flaw, aka “The Return of the WIZard,” affects versions 4.87 to 4.91 of the Exim mail transfer agent (MTA) software. The issue could be exploited by unauthenticated remote attackers to execute arbitrary commands on mail servers for some non-default server configurations.
The flaw resides in the deliver_message() function in /src/deliver.c and it is caused by the improper validation of recipient addresses. The issue could lead to remote code execution with root privileges on the mail server.
“Russian military cyber actors, publicly known as Sandworm Team, have been exploiting a vulnerability in Exim mail transfer agent (MTA) software since at least last August.” reads the advisory published by the NSA. “The Russian actors, part of the General Staff Main Intelligence Directorate’s (GRU) Main Center for Special Technologies (GTsST), have used this exploit to add privileged users, disable network security settings, execute additional scripts for further network exploitation; pretty much any attacker’s dream access – as long as that network is using an unpatched version of Exim MTA.”
“NSA adds its encouragement to immediately patch to mitigate against this still current threat.”
GRU Main Center for Special Technologies (GTsST) hackers of
Hackers belonging to the Unit 74455, under the Russian GRU Main Center for Special Technologies (GTsST), are exploiting the Exim issue after an update was issued in June 2019.
“The actors exploited victims using Exim software on their public facing MTAs by sending a command in the “MAIL FROM” field of an SMTP (Simple Mail Transfer Protocol) message.” states the advisory.
Below a sample “MAIL FROM” exploitation command published by the NSA:
Russian state-sponsored hackers leverage the vulnerability to download a shell script from a domain under their control and use it to “add privileged users, disable network security settings, update SSH configurations to enable additional remote access, execute an additional script to enable follow-on exploitation.”
NSA recommends patching Exim servers immediately by installing version 4.93 or newer.
“Update Exim immediately by installing version 4.93 or newer to mitigate this and other vulnerabilities. Other vulnerabilities exist and are likely to be exploited, so the latest fully patched version should be used. Using a previous version of Exim leaves a system vulnerable to exploitation. System administrators should continually check software versions and update as new versions become available.” concludes NSA. “Administrators can update Exim Mail Transfer Agent software through their Linux distribution’s package manager or by downloading the latest version from https://exim.org/mirrors.html.”
NSA’s advisory also includes Indicators of Compromise and instructions on how to detect exploit attempts and unauthorized changes.
Unfortunately, the number of vulnerable Exim installs exposed online is still high, querying Shodan for installs exposed online we can more than 2,481,000 servers, with more than 2,400,000 servers running the patched Exim 4.93 release.
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(SecurityAffairs – APT, hacking)
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Text extracted automatically; images, tables and formatting may be missing. Original: https://securityaffairs.com/103948/apt/nsa-sandworm-exim-attacks.html