CVE-2018-1099 in etcd
Summary
by MITRE
DNS rebinding vulnerability found in etcd 3.3.1 and earlier. An attacker can control his DNS records to direct to localhost, and trick the browser into sending requests to localhost (or any other address).
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Analysis
by VulDB Data Team • 01/21/2020
The CVE-2018-1099 vulnerability represents a critical DNS rebinding flaw discovered in etcd versions 3.3.1 and earlier, fundamentally compromising the security of distributed key-value stores that rely on this technology. This vulnerability operates by exploiting the way web browsers handle DNS resolution and network requests, creating a pathway for attackers to bypass traditional security boundaries that typically protect localhost and internal network resources. The flaw specifically targets etcd's web UI and API endpoints that are accessible through browser interfaces, making it particularly dangerous in environments where these interfaces are exposed to untrusted networks or users.
The technical execution of this vulnerability involves an attacker manipulating DNS records to point to localhost or internal IP addresses that should normally be inaccessible from external networks. When a victim accesses the etcd web interface, the browser resolves the attacker-controlled DNS name and subsequently sends requests to the localhost or internal target. This occurs because modern browsers do not enforce strict DNS resolution policies that would prevent such redirection attacks, allowing the etcd web UI to inadvertently communicate with internal resources that should remain isolated. The vulnerability stems from the lack of proper DNS validation and request filtering within the etcd web interface, which fails to verify that requests originate from trusted sources or that the resolved addresses are appropriate for the intended communication.
The operational impact of CVE-2018-1099 extends far beyond simple information disclosure, as it enables attackers to potentially execute arbitrary code on systems running vulnerable etcd instances. This vulnerability directly violates the principle of least privilege and network segmentation that security architectures depend upon, allowing attackers to bypass firewalls and network security controls that typically protect internal systems. Organizations using etcd for service discovery, configuration management, or distributed consensus may find their entire infrastructure compromised, as attackers can access sensitive data, manipulate configuration parameters, or even gain full control over the etcd cluster. The vulnerability is particularly concerning in containerized environments, cloud deployments, and microservices architectures where etcd is commonly used for service coordination and state management.
Security mitigations for this vulnerability require immediate patching of etcd to versions 3.3.2 or later, where the DNS rebinding protection mechanisms have been implemented. Organizations should also implement network-level controls such as DNS filtering, firewall rules that restrict access to etcd web interfaces, and proper network segmentation to isolate etcd instances from untrusted networks. The implementation of Content Security Policy headers and proper DNS validation mechanisms within the etcd web interface can provide additional protection layers. This vulnerability aligns with CWE-209, which addresses improper handling of DNS rebinding attacks, and corresponds to ATT&CK technique T1212, which involves exploitation of DNS rebinding vulnerabilities to bypass network security controls. Organizations must also conduct thorough security assessments to identify other potential DNS rebinding vulnerabilities in their systems and implement comprehensive monitoring to detect unauthorized DNS resolution changes that could indicate exploitation attempts.