CVE-2018-1043 in Moodle
Summary
by MITRE
In Moodle 3.x, the setting for blocked hosts list can be bypassed with multiple A record hostnames.
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Analysis
by VulDB Data Team • 02/02/2023
The vulnerability identified as CVE-2018-1043 affects Moodle version 3.x platforms and represents a significant security flaw in the system's network access control mechanisms. This issue specifically targets the blocked hosts list functionality that administrators configure to restrict external connections from Moodle instances. The vulnerability arises from a design flaw in how Moodle processes hostname resolution when multiple A records are present for a single domain name, allowing malicious actors to circumvent intended network restrictions through DNS manipulation techniques.
The technical implementation of this vulnerability stems from Moodle's handling of DNS resolution for hostnames in the blocked hosts configuration. When a hostname resolves to multiple A records through DNS, the system fails to properly validate all resolved addresses against the configured block list. This occurs because the application typically processes only the first resolved IP address or does not maintain proper state tracking across all A record resolutions. The flaw creates a bypass condition where an attacker can register a domain with multiple A records, where one record points to a blocked IP address and another points to an allowed IP address, effectively allowing access through the blocked host restriction.
From an operational impact perspective, this vulnerability presents a serious threat to organizations relying on Moodle for educational content management and learning platform services. Attackers could exploit this weakness to gain unauthorized access to external resources that should be blocked, potentially leading to data exfiltration, malicious code execution, or lateral movement within network environments. The vulnerability undermines the fundamental security controls that administrators implement to protect their learning management systems from connecting to potentially harmful external domains, creating an attack surface that could be leveraged for more sophisticated compromise techniques.
The security implications extend beyond simple access bypass, as this vulnerability aligns with several ATT&CK framework techniques including T1071.004 Application Layer Protocol: DNS and T1046 Network Service Scanning, where attackers can manipulate DNS responses to evade network restrictions. Additionally, this flaw relates to CWE-284 Improper Access Control, as it represents a failure in access control enforcement mechanisms. Organizations using Moodle should implement immediate mitigations including updating to patched versions of Moodle, reviewing and strengthening DNS security measures, and monitoring for suspicious network activity patterns that might indicate exploitation attempts. The vulnerability also highlights the importance of proper input validation and DNS resolution handling in web applications, particularly those with network access control requirements.