A new critical flaw in Exim exposes email servers to remote 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% |
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| 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 article427 words · extracted from securityaffairs.com · click to collapse
Pierluigi Paganini
September 30, 2019
Exim maintainers released an urgent security update to address a critical security flaw that could allow a remote attacker to potentially execute malicious code on targeted servers.
Exim maintainers released an urgent security update, Exim version 4.92.3, to address a critical security vulnerability that could allow a remote attacker to crash or potentially execute malicious code on targeted email servers.
The flaw is a heap-based buffer overflow, tracked as CVE-2019-16928, that resides in the string_vformat (string.c). An attacker could exploit the flaw using an extraordinary long EHLO string to crash the Exim process that is receiving the message.
“There is a heap-based buffer overflow in string_vformat (stringc). The currently known exploit uses extraordinary long EHLO string to crash the Exim process that is receiving the message. While this mode of operation Exim already dropped its privileges, other paths to reach the vulnerable code may exist.” reads the security advisory published by the maintainers.
The CVE-2019-16928 flaw was reported by Jeremy Harris of Exim Development Team, it affects all versions of the Exim email server software from 4.92 up to and the version 4.92.2. The expert also released a PoC exploit for this vulnerability.
Early September, the Exim development team has addressed another vulnerability in the popular mail server, tracked as CVE-2019-15846. The vulnerability could be exploited by local and remote attackers to execute arbitrary code with root privileges.
The vulnerability is a heap overflow that affects version 4.92.1 and prior of Exim mail server that accepts TLS connections. The vulnerability affects both GnuTLS and OpenSSL.
In mid-June, researchers observed several threat actors exploiting another flaw in the popular software, tracked as CVE-2019-10149, that 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. The CVE-2019-10149 flaw was addressed the Exim’s development team with the release of version 4.92 in February.
The flaw is easily exploitable by a local and a remote attacker in certain non-default configurations, experts believe that threat actors will start using it in attacks in the wild.
Exim also patched a severe remote command execution vulnerability (CVE-2019-10149) in its email software that was actively exploited in the wild by various groups of hackers to compromise vulnerable servers.
The major Linux distributions, including Ubuntu, Arch Linux, FreeBSD, Debian, and Fedora, already released security updates.
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(SecurityAffairs – Mail Server, hacking)
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Text extracted automatically; images, tables and formatting may be missing. Original: https://securityaffairs.com/91914/hacking/exim-critical-flaw.html