Nginx 1.8.1, a widely-used web server powering over 342 websites, contains two significant security vulnerabilities in its DNS resolver functionality. These flaws can allow remote attackers to crash your server or consume excessive resources without authentication. Understanding these CVEs is essential for maintaining your website's security and uptime, as exploitation requires minimal effort from attackers.
This comprehensive guide will walk you through identifying whether your server is affected, understanding the risks, and implementing the necessary patches. We'll break down the technical details into actionable steps that even non-technical website owners can follow.
Protecting your infrastructure from these vulnerabilities should be a priority, as they directly impact your server's stability and performance. Let's explore what you need to know about Nginx 1.8.1 security.
What is Nginx 1.8.1?
Nginx is one of the most popular web server software solutions globally, used to serve websites and handle web traffic efficiently. Think of it as the digital infrastructure that delivers your website to visitors' browsers. Nginx 1.8.1 is a specific version released to address various security concerns, but unfortunately, it still contains vulnerabilities that need attention. Many organizations use this version due to stability requirements or legacy system constraints.
The vulnerabilities in Nginx 1.8.1 specifically affect the DNS resolver—the component responsible for translating domain names into IP addresses. When improperly configured or exploited, attackers can send specially crafted DNS responses that cause the server to malfunction. These flaws demonstrate why keeping your server software updated and monitored is crucial for maintaining a secure online presence.
Key Vulnerabilities in Nginx 1.8.1
2 CVEs found. The most critical are explained below.
HIGHCVE-2016-07427.5/10 · CVSS v3.1
⏱ Immediate
Nginx DNS Crash Vulnerability
Nginx has a weakness in how it processes DNS responses from the internet. An attacker can send a specially crafted DNS response that causes Nginx to crash and stop working. This is a critical flaw because your website depends on Nginx to stay online.
Impact: Your website could go offline suddenly and repeatedly as the Nginx service crashes. Visitors won't be able to access your site, resulting in lost business and damaged reputation.
MEDIUMCVE-2016-07475.3/10 · CVSS v3.1
⏱ Within 7 days
Nginx DNS Resource Overload Vulnerability
Nginx's DNS resolver doesn't properly control how many DNS lookups it will perform. An attacker can exploit this by triggering excessive DNS resolution attempts, consuming all of your server's resources. Your website slows down or becomes unresponsive even without a complete crash.
Impact: Your website will become extremely slow or unresponsive, causing visitors to leave and damaging user experience. This reduces revenue and increases support complaints.
1Access your server via SSH terminal or control panel and run the command: nginx -v to display your current Nginx version
2If the output shows version 1.8.1 or earlier, your server is potentially vulnerable to CVE-2016-0742 and CVE-2016-0747
3Check your Nginx configuration file (typically located at /etc/nginx/nginx.conf) to see if DNS resolver is enabled by searching for 'resolver' directives
How to Fix These Vulnerabilities
1Update Nginx to version 1.8.2 or higher (or 1.9.10+ if using the 1.9.x branch) by running your system's package manager: sudo apt-get update && sudo apt-get install nginx (on Ubuntu/Debian) or sudo yum update nginx (on CentOS/RHEL)
2After installation, verify the new version: nginx -v should show version 1.8.2 or later
3If you use DNS resolution in your Nginx configuration, implement additional security measures such as rate limiting DNS queries and validating resolver responses in your nginx.conf file
4Restart the Nginx service to apply all changes: sudo systemctl restart nginx or sudo service nginx restart, then verify your website is still accessible
Conclusion
The DNS resolver vulnerabilities in Nginx 1.8.1 (CVE-2016-0742 and CVE-2016-0747) pose real risks to your server's availability and performance. While these CVEs are relatively old, many legacy systems still run this version, making them potential targets for attackers. Taking action to upgrade your server is not just a security best practice—it's essential for protecting your online business.
Securing your web infrastructure doesn't have to be complicated. Use SiteRecipe.com's vulnerability scanner to automatically detect outdated software versions and security flaws across your entire website ecosystem. Our platform identifies vulnerabilities like these Nginx CVEs in seconds and provides step-by-step remediation guidance. Start your free security assessment today and ensure your server is protected against known threats.
Frequently Asked Questions
What happens if my server runs Nginx 1.8.1 and gets attacked?
If attacked, your Nginx worker processes could crash, causing your website to become unavailable. In the CVE-2016-0742 attack, malicious DNS responses trigger invalid pointer dereferences that destabilize the server. The CVE-2016-0747 flaw could exhaust server resources, slowing down or stopping legitimate user access to your website.
Does updating Nginx require downtime?
Most hosting providers can update Nginx with zero or minimal downtime by using rolling restarts or temporary traffic redirection. Contact your hosting support to understand their specific update process. For self-managed servers, you can typically restart Nginx in seconds with proper configuration testing beforehand.
Are there temporary workarounds if I can't update immediately?
Yes, you can disable the DNS resolver feature in your nginx.conf if it's not essential for your application. However, this is only a temporary solution—updating to a patched version (1.8.2+) is the proper fix. You can also implement firewall rules to restrict DNS traffic and monitor your server logs for suspicious activity.
How can I monitor for exploitation attempts?
Check your Nginx error logs (usually at /var/log/nginx/error.log) for crash patterns or worker process exits. Implement server monitoring tools to track CPU and memory usage spikes. SiteRecipe.com's monitoring features can alert you to abnormal server behavior that may indicate attack attempts.
Will upgrading break my current website configuration?
Nginx versions 1.8.2 and later maintain backward compatibility with 1.8.1 configurations in most cases. Your website should continue working without changes. Test the update on a staging server first if you have critical custom configurations, then apply it to production with confidence.
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DISCLAIMER: This report is based on publicly available CVE data from the National Vulnerability
Database (NVD) maintained by NIST. Detection of a technology version does not confirm active
exploitation on any specific website. For informational purposes only.
SiteRecipe is not responsible for actions taken based on this report.
Always consult a qualified security professional.