Exim Buffer Overflow RCE Vulnerability (CVE-2018-6789) – What You Need to Know
On February 10, the Unix-based email server Exim released an update to address a heap buffer overflow vulnerability that can be used by an unauthenticated attacker to remotely execute arbitrary code. The flaw, assigned CVE-2018-6789, is noted to exist in all versions of Exim, prior to their latest release, 4.90.1, which means the attack surface potential is very wide. A quick search on Shodan yields more than 6 million results.
Vulnerability details
The vulnerability was originally discovered by DEVCORE, and details were published on their blog on March 6. The vulnerability is due to a flaw in the b64decode buffer length in the base64d() function. Due to an off-by-one calculation mistake, heap memory can be overwritten when parsing an invalid base64 string leading to critical data being overwritten.
As base64 decoding is a widely used function, and since the byte is user-controlled, this increases the ease of exploitation, which can be utilized for remote code execution.
Identifying affected systems
To detect systems affected by this critical flaw, Tenable has released Nessus® plugins for Tenable.io Vulnerability Management, SecurityCenter and Nessus Pro. Additionally, Tenable has released passive detection via Nessus Network Monitor, which may be used with Tenable.io Vulnerability Management to detect the vulnerability passively on the network. Tenable.io Container Security has also been updated to detect the Exim off-by-one RCE vulnerability in Docker container images. The following table summarizes Tenable's coverage.
|
Plugin ID |
Description |
|
107149 |
Exim < 4.90.1 Buffer Overflow RCE Vulnerability |
|
700223 (Nessus Network Monitor) |
Exim < 4.90.1 Remote Code Execution |
|
106722 |
Debian DLA-1274-1 : exim4 security update |
|
106728 |
Debian DSA-4110-1 : exim4 - security update |
|
107007 |
Fedora 26 : exim (2018-25a7ba3cb6) |
|
107009 |
Fedora 27 : exim (2018-5aec14e125) |
|
106733 |
FreeBSD : exim -- a buffer overflow vulnerability, remote code execution (316b3c3e-0e98-11e8-8d41-97657151f8c2) |
|
106888 |
openSUSE Security Update : exim (openSUSE-2018-170) |
|
106791 |
Ubuntu 14.04 LTS / 16.04 LTS / 17.10 : exim4 vulnerability (USN-3565-1) |
|
107178 |
GLSA-201803-01 : Exim: Multiple vulnerabilities |
What should you do?
If you’re running a version of Exim prior to 4.90.1, make sure you update to the most current release. Exim notes that all versions of Exim prior to 4.90.1 are now obsolete and that 3.x releases are also obsolete and should not be used.
Get more information
- Learn more about Tenable.io, the first Cyber Exposure platform for holistic management of your modern attack surface
- Get a free 60-day trial of Tenable.io Vulnerability Management
- DEVCORE blog details
- Exim ChangeLog
- Exim CVE-2018-6789 Advisory
Related Articles
Do You Think You Have No AI Exposures? Think Again
August 6, 2024As AI usage becomes more prevalent in organizations globally, security teams must get full visibility into these applications. Building a comprehensive inventory of AI applications in your environment is a first step. Read on to learn what we found about AI application-usage in the real world when we analyzed anonymized telemetry data from scans using Tenable’s products.
Never Trust User Inputs -- And AI Isn't an Exception: A Security-First Approach
August 6, 2024As AI transforms industries, security remains critical. Discover the importance of a security-first approach in AI development, the risks of open-source tools, and how Tenable's solutions can help protect your systems.
Cybersecurity Snapshot: Prompt Injection and Data Disclosure Top OWASP’s List of Cyber Risks for GenAI LLM Apps
November 22, 2024Don’t miss OWASP’s update to its “Top 10 Risks for LLMs” list. Plus, the ranking of the most harmful software weaknesses is out. Meanwhile, critical infrastructure orgs have a new framework for using AI securely. And get the latest on the BianLian ransomware gang and on the challenges of protecting water and transportation systems against cyberattacks.
Active Directory Under Attack: Five Eyes Guidance Targets Crucial Security Gaps
November 21, 2024A landmark global report from cybersecurity agencies emphasizes 17 attack techniques against Microsoft Active Directory and cautions organizations to step up protections. In the first of our two-part series, we offer five steps you can take today to shore up your AD defenses.
Five Cyber Agencies Sound Alarm About Active Directory Attacks: Beyond the Basics
November 21, 2024A landmark global report emphasizes 17 attack techniques against Microsoft Active Directory and cautions organizations to step up protections. In the second of our two-part series, we take you beyond the basics to highlight three key areas to focus on.
- Plugins