Exim TLS Flaw Opens Email Servers to Remote 'Root' Code Execution 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% |
| — |
Full article416 words · extracted from thehackernews.com · click to collapse
The Hacker NewsSep 06, 2019
A critical remote code execution vulnerability has been discovered in the popular open-source Exim email server software, leaving at least over half a million email servers vulnerable to remote hackers.
Exim maintainers today released Exim version 4.92.2 after publishing an early warning two days ago, giving system administrators a heads-up on its upcoming security patches that affect all versions of the email server software up to and including then-latest 4.92.1.
Exim is a widely used, open source mail transfer agent (MTA) software developed for Unix-like operating systems such as Linux, Mac OSX or Solaris, which runs almost 60% of the internet's email servers today for routing, delivering and receiving email messages.
Tracked as CVE-2019-15846, the security vulnerability only affects Exim servers that accept TLS connections, potentially allowing attackers to gain root-level access to the system "by sending an SNI ending in a backslash-null sequence during the initial TLS handshake."
SNI, stands for Server Name Indication, is an extension of the TLS protocol that allows the server to safely host multiple TLS certificates for multiple sites, all under a single IP address.
According to the Exim team, since the vulnerability doesn't depend on the TLS library being used by the server, both GnuTLS and OpenSSL are affected.
Moreover, though the default configuration of the Exim mail server software doesn't come with TLS enabled, some operating systems bundled the Exim software with the vulnerable feature enabled by default.
The vulnerability was discovered by an open source contributor and security researcher who goes by the online alias Zerons and analyzed by cybersecurity experts at Qualys.
Just three months ago, Exim also patched a severe remote command execution vulnerability, tracked as CVE-2019-10149, that was actively exploited in the wild by various groups of hackers to compromise vulnerable servers.
The Exim advisory says that a rudimentary proof of concept (PoC) exists for this flaw, but currently there is no known exploit available to the public.
Server administrators are highly recommended to install the latest Exim 4.92.2 version immediately, and if not possible, can mitigate the issue by not allowing unpatched Exim servers to accept TLS connections.
The team says, "If you can't install the above versions, ask your package maintainer for a version containing the backported fix. On request and depending on our resources we will support you in backporting the fix."
Found this article interesting? Follow us on Google News, Twitter and LinkedIn to read more exclusive content we post.
Text extracted automatically; images, tables and formatting may be missing. Original: https://thehackernews.com/2019/09/exim-email-server-vulnerability.html