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January 30, 2025
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How to Fix CVE-2024-11187: CPU Exhaustion Vulnerability in BIND 9 Servers?
The Domain Name System (DNS) is a critical component of the internet infrastructure, and the BIND 9 server is one of the most widely used DNS server implementations. A recently disclosed vulnerability, CVE-2024-11187, poses a significant threat to BIND 9 servers by potentially causing CPU exhaustion. This vulnerability can be exploited remotely by crafting specific DNS queries, leading to denial-of-service conditions. This article aims to provide security professionals with a comprehensive understanding of the flaw and practical guidance on how to remediate and mitigate it. We will discuss the vulnerability, its impact, affected versions, and provide clear steps for securing your BIND 9 servers.
A Short Introduction to BIND 9
BIND (Berkeley Internet Name Domain) is an open-source DNS server software that is widely used across the internet to translate domain names into IP addresses. It’s a foundational technology for internet operations and is critical for almost all services. BIND 9 is the latest version of the software, offering many advanced features and improvements. It acts as both an authoritative name server, providing DNS information for specified domains, and a recursive resolver, querying other name servers to resolve DNS requests. Because of its central role in DNS infrastructure, vulnerabilities in BIND 9 can have widespread and severe impacts. Therefore, it is essential to keep BIND 9 servers updated and properly configured to minimize risks.
Summary of CVE-2024-11187
CVE ID: CVE-2024-11187
Description: A vulnerability that causes CPU exhaustion due to processing numerous records in the additional section of a DNS response.
CVSS Score: 7.5
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVE-2024-11187 arises from how BIND 9 handles DNS responses with many records in the additional section. Specifically, a maliciously crafted DNS zone can be created such that queries to this zone result in responses that contain a large number of records in the "additional section." An attacker who sends numerous such queries can cause either the authoritative server or an independent resolver to expend disproportionate CPU resources. This excessive resource consumption can lead to a denial-of-service (DoS) condition, effectively preventing the BIND server from responding to other legitimate queries. The vulnerability is exploitable remotely and does not require any special privileges or user interaction. The primary reason for this flaw is the inefficient processing of numerous additional records, which can be exploited by sending specially crafted queries.
Impact of the Vulnerability
The impact of CVE-2024-11187 is significant as it can lead to a complete denial of service for BIND 9 servers. A vulnerable BIND 9 instance can be forced to consume excessive CPU resources, eventually reaching a point where it cannot respond to other client queries. This can severely disrupt services that rely on DNS resolution. While the issue can primarily affect resolvers due to the nature of queries they process, authoritative servers are also vulnerable, which could affect the performance of services hosted on those servers. The resource exhaustion can cascade into other dependent network services leading to wider impact. The ability to remotely trigger this vulnerability makes it particularly dangerous as an attacker can easily launch a DoS attack against BIND servers without requiring any prior access or authentication. This vulnerability is a high-priority security issue that needs to be addressed promptly to ensure the availability and stability of the DNS infrastructure.
Products Affected by the Vulnerability
The following BIND 9 versions are affected by this vulnerability:
|
Product
|
Affected Versions
|
|---|---|
|
BIND
|
9.11.0 → 9.11.37,
9.16.0 → 9.16.50,
9.18.0 → 9.18.32,
9.20.0 → 9.20.4,
9.21.0 → 9.21.3
|
|
BIND Supported Preview Edition
|
9.11.3-S1 → 9.11.37-S1,
9.16.8-S1 → 9.16.50-S1,
9.18.11-S1 → 9.18.32-S1
|
Note: Versions prior to 9.11.0 and 9.11.3-S1 were not assessed and may also be affected. The vulnerability affects both authoritative servers and resolvers.
How to Check if Your Product is Vulnerable?
To determine if your BIND 9 server is vulnerable to CVE-2024-11187, consider the following methods:
Version Check: The most straightforward method is to check the installed version of BIND 9. You can usually do this by running the command
named -v or rndc -von your server. Compare the reported version with the affected versions listed above. If your version falls within the listed ranges, your server is vulnerable.Monitor CPU Usage: Keep a close watch on the CPU usage of your BIND server. If you see unusually high CPU utilization, especially when processing DNS queries, it could indicate an exploitation attempt.
DNS Query Analysis: You could attempt to craft queries that could trigger this vulnerability using a test server. Monitor the CPU usage when you execute the malicious queries.
Network Monitoring: Monitor network traffic for unusual patterns of DNS queries to the same domains.
Log Analysis: Review the logs of your BIND server for suspicious activity, high rates of responses with a large number of additional records could be an indicator.
Vulnerability Scanners: Employ vulnerability scanners to scan your BIND servers to automatically detect this flaw. Ensure the tool is updated to detect the latest vulnerabilities.
How to Fix the Vulnerability?
To mitigate and remediate CVE-2024-11187, the primary recommendation is to upgrade to a patched version of BIND 9. Here are the steps you should take:
Upgrade BIND 9:
Upgrade to the patched release that most closely matches your current BIND 9 version. The patched versions are:
- 9.18.33
- 9.20.5
- 9.21.4
- 9.18.33-S1 (For BIND Supported Preview Edition)
Download the appropriate version from the official ISC (Internet Systems Consortium) website.
Follow the upgrade instructions specific to your operating system.
2. Workaround:
If upgrading is not immediately possible, you can implement the workaround by setting the
minimal-responses yes;option in yournamed.confconfiguration file. This option significantly reduces the number of records included in the additional section of the DNS response, thus mitigating the CPU exhaustion.After applying this change, restart the
namedservice.
3. Additional Security Measures:
Rate Limiting: Implement rate limiting on your DNS server to restrict the number of queries from a single source, which can help to mitigate denial-of-service attacks.
Firewall Rules: Configure your firewall to block traffic from suspicious sources or IP addresses that are known to be involved in malicious activity.
Monitoring: Implement regular monitoring of the BIND 9 server CPU utilization, network traffic, and logs. Use alerts to track and respond to unusual activity promptly.
Regular Updates: Establish a routine process for applying security patches and software updates to all your DNS servers to minimize your exposure to similar vulnerabilities.
Input Validation: Ensure proper input validation when handling DNS requests, particularly when processing the additional records, this can help to minimize the impact of flaws.
Network Segmentation: Isolating your DNS infrastructure on a separate network segment is a great practice to isolate the impact in case of a vulnerability.
DNSSEC: Implement DNSSEC to secure DNS responses to protect against any tampering of the DNS records.
By upgrading to the patched versions and implementing the above security best practices, you can significantly reduce the risk of your BIND 9 servers being exploited by CVE-2024-11187. It is essential to act proactively to protect the integrity and reliability of your DNS infrastructure. You should also consider using a vulnerability assessments strategy to identify and prioritize system risks, to protect from similar kinds of vulnerabilities. You can also use SOAR for threat detection and incident response to automate the response process, for similar cases. Make sure you understand what are the different types of pki certificates to strengthen your network security. Also, you should always have a cyber incident response plan.
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Arun KL
Arun KL is a cybersecurity professional with 15+ years of experience in IT infrastructure, cloud security, vulnerability management, Penetration Testing, security operations, and incident response. He is adept at designing and implementing robust security solutions to safeguard systems and data. Arun holds multiple industry certifications including CCNA, CCNA Security, RHCE, CEH, and AWS Security.
