Russia-linked APT exploited at least 3 Exim flaws in recent attacks
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 | |
| CVE-2019-15846 | Exim before 4.92.2 allows remote attackers to execute arbitrary code as root via a trailing backslash. Exim before 4.92.2 allows remote attackers to execute arbitrary code as root via a trailing backslash. NVD description · AI analysis pending | 9.8 | 36% |
| — | ||
| CVE-2019-16928 | Exim Out-of-bounds Write Vulnerability Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846. There is a heap-based buffer overflow in string_vformat in string.c involving a long EHLO command. NVD description · AI analysis pending | 9.8 | 42% | KEV PoC ×2 |
| — |
Full article385 words · extracted from securityaffairs.com · click to collapse
Several flaws in the Exim mail transfer agent (MTA) have been exploited by Russia-linked hackers, hundreds of thousands of servers are still unpatched.
Russia-linked threat actors have exploited several vulnerabilities in the Exim mail transfer agent (MTA) in their campaigns.
Last week, the U.S. National Security Agency (NSA) warned that Russia-linked APT group tracked Sandworm Team has been exploiting a critical vulnerability (CVE-2019-10149) in the Exim mail transfer agent (MTA).
According to the NSA, hackers belonging to the Unit 74455, under the Russian GRU Main Center for Special Technologies (GTsST), are exploiting the CVE-2019-10149 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.
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.
Now security firm RiskIQ revealed that threat actors had exploited two other Exim vulnerabilities in the same campaign. The two issues are:
- a remote code execution vulnerability tracked as CVE-2019-15846, it impacts version 4.92.1 and earlier and was patched in September 2019;
- a DoS and code execution flaw tracked as CVE-2019-16928, it impacts versions 4.92 through 4.92.2.
In May, RiskIQ experts identified more than 900,000 vulnerable Exim servers. Most of the servers were running version 4.92, this means that they were patched against the CVE-2019-10149 issue, while they were still impacted by the other two vulnerabilities.
Experts noticed that many servers were updated in May, but there are still hundreds of thousands of vulnerable servers.
“The vulnerabilities leveraged impact Exim Internet Mailer version 4.87 – 4.92. Searching RiskIQ’s internet intelligence database, from May 1, 2020, RiskIQ has observed over 900K vulnerable Exim instances.” reads the analysis published by RiskIQ.
Querying Shodan search engine for vulnerable Exim servers we can verify that there are more than 250,000 installs running version 4.91 and over one million servers running version 4.92.
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(SecurityAffairs – hacking, cybersecurity)
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