CVE-2011-1922 in Unbound
Summary
by MITRE
daemon/worker.c in Unbound 1.x before 1.4.10, when debugging functionality and the interface-automatic option are enabled, allows remote attackers to cause a denial of service (assertion failure and daemon exit) via a crafted DNS request that triggers improper error handling.
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Analysis
by VulDB Data Team • 12/02/2024
The vulnerability identified as CVE-2011-1922 affects the Unbound DNS resolver version 1.x before 1.4.10, specifically within the daemon/worker.c component. This flaw manifests when both debugging functionality and the interface-automatic option are enabled simultaneously, creating a dangerous condition that remote attackers can exploit to trigger a denial of service. The vulnerability stems from improper error handling mechanisms that fail to adequately validate incoming DNS requests, particularly those crafted to manipulate the debugging state of the daemon process.
The technical implementation of this vulnerability involves the interaction between multiple system components within Unbound's architecture. When debugging is enabled alongside the interface-automatic feature, the daemon maintains certain internal state information that becomes corrupted when processing malformed DNS requests. The assertion failure occurs during the worker thread processing of these crafted packets, where the system attempts to validate data structures that have been manipulated through the malicious input. This improper error handling causes the daemon to terminate unexpectedly, resulting in a complete service disruption that affects all DNS resolution capabilities for the affected system.
From an operational perspective, this vulnerability represents a significant risk to network infrastructure relying on Unbound as their DNS resolver. The remote nature of the attack means that adversaries can exploit this weakness from any network location without requiring local access or authentication credentials. The denial of service impact is severe as it completely terminates the DNS daemon service, potentially causing cascading failures throughout dependent network services that rely on proper DNS resolution. Organizations using Unbound with debugging enabled and automatic interface detection would be particularly vulnerable, as these configurations are common in development and testing environments where security hardening might be overlooked.
The vulnerability aligns with CWE-248, which addresses "Uncaught Exception" conditions in software systems, and demonstrates how improper error handling can lead to system termination rather than graceful degradation. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to "Endpoint Denial of Service" through the manipulation of daemon processes. The exploitability factor is relatively low to moderate as it requires specific configuration conditions to exist, but the impact is high severity due to the complete service disruption. Organizations should implement immediate mitigations including disabling debugging functionality when not actively required, updating to Unbound version 1.4.10 or later, and ensuring that the interface-automatic option is not enabled in production environments where remote attacks are possible.
Security practitioners should conduct comprehensive audits of Unbound configurations across their networks to identify systems with debugging enabled and automatic interface detection active. The recommended remediation path involves upgrading to patched versions of Unbound, disabling unnecessary debugging features, and implementing proper network segmentation to limit exposure to untrusted networks. Additionally, monitoring systems should be configured to detect unusual daemon termination events that could indicate exploitation attempts, as these incidents may precede more sophisticated attacks targeting the DNS infrastructure.