CONFERENCE On Demand: Cyber AI & Automation Summit - Watch Now
Connect with us

Hi, what are you looking for?


Email Security

Exim Vulnerability Allows Remote Code Execution as Root

Exim mail servers are vulnerable to attacks due to a security hole that allows a local or remote attacker to execute arbitrary code with root privileges.

Exim mail servers are vulnerable to attacks due to a security hole that allows a local or remote attacker to execute arbitrary code with root privileges.

According to Exim developers, the vulnerability, tracked as CVE-2019-15846, affects version 4.92.1 and prior. Exim 4.92.2, first announced on Wednesday and released on Friday, should patch the flaw.

The vulnerability, described as a heap overflow, affects Exim servers that accept TLS connections, and exploitability is not dependent on the TLS library used — developers note that both GnuTLS and OpenSSL are affected.

“The vulnerability is exploitable by sending a SNI ending in a backslash-null sequence during the initial TLS handshake,” Exim developers said in an advisory.

While there is no evidence of malicious exploitation, Qualys researchers, who have analyzed the flaw, have developed a basic proof-of-concept (PoC) exploit to demonstrate that the heap overflow is exploitable. The issue was initially reported to Exim developers on July 21 by a researcher who uses the online moniker “Zerons.”

Exploitation of the vulnerability can be prevented by configuring the server to not accept TLS connections, but this mitigation is not recommended. Another mitigation involves adding specific rules to the access control list (ACL).

“This is a buffer overflow vulnerability. It does not directly allow attackers to execute commands as root. This flaw ultimately allows attackers to overwrite memory which can be used to achieve code execution. This is substantially different from a remote command execution because the attacker must overcome not only obstacles from the vulnerable program’s implementation but also from OS exploit mitigations,” Craig Young, computer security researcher for Tripwire’s Vulnerability and Exposure Research Team, told SecurityWeek.

“Due to the various complexities involved in crafting a reliable cross-platform exploit, it does not seem likely to me that we will quickly see active code execution attack campaigns by script kiddies. That being said, I would be surprised if more sophisticated attackers are not already using this to exploit specifically targeted mail servers,” Young added.

Advertisement. Scroll to continue reading.

Exim is one of the most widely used mail servers and Shodan shows over 5 million instances, a majority in the United States. This makes Exim a tempting target for malicious actors.

In mid-June, security experts and companies warned that CVE-2019-10149, an Exim vulnerability that had been patched earlier that month, was being exploited to deliver cryptocurrency miners.

*updated with comments from Tripwire’s Craig Young

Related: Critical Code Execution Flaw Found in Exim

Related: ProFTPD Vulnerability Can Expose Servers to Attacks

Related: Several Vulnerabilities Patched in nginx

Written By

Eduard Kovacs (@EduardKovacs) is a managing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.

Click to comment

Daily Briefing Newsletter

Subscribe to the SecurityWeek Email Briefing to stay informed on the latest threats, trends, and technology, along with insightful columns from industry experts.

Join us as we delve into the transformative potential of AI, predictive ChatGPT-like tools and automation to detect and defend against cyberattacks.


As cybersecurity breaches and incidents escalate, the cyber insurance ecosystem is undergoing rapid and transformational change.


Expert Insights

Related Content


Less than a week after announcing that it would suspended service indefinitely due to a conflict with an (at the time) unnamed security researcher...

Data Breaches

OpenAI has confirmed a ChatGPT data breach on the same day a security firm reported seeing the use of a component affected by an...

Risk Management

The supply chain threat is directly linked to attack surface management, but the supply chain must be known and understood before it can be...

IoT Security

A group of seven security researchers have discovered numerous vulnerabilities in vehicles from 16 car makers, including bugs that allowed them to control car...


A researcher at IOActive discovered that home security systems from SimpliSafe are plagued by a vulnerability that allows tech savvy burglars to remotely disable...


Patch Tuesday: Microsoft calls attention to a series of zero-day remote code execution attacks hitting its Office productivity suite.


Patch Tuesday: Microsoft warns vulnerability (CVE-2023-23397) could lead to exploitation before an email is viewed in the Preview Pane.


The latest Chrome update brings patches for eight vulnerabilities, including seven reported by external researchers.