CVE-2011-4528 in Unbound
Summary
by MITRE
Unbound before 1.4.13p2 attempts to free unallocated memory during processing of duplicate CNAME records in a signed zone, which allows remote DNS servers to cause a denial of service (daemon crash) via a crafted response.
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Analysis
by VulDB Data Team • 08/08/2024
The vulnerability identified as CVE-2011-4528 represents a critical memory management flaw in the Unbound DNS resolver software that existed prior to version 1.4.13p2. This issue specifically manifests when the DNS resolver encounters duplicate CNAME records within signed DNS zones, creating a condition where the software attempts to free memory that was never properly allocated. The flaw operates at the intersection of DNS security mechanisms and memory management protocols, exploiting the interaction between DNS security extensions and the resolver's handling of duplicate record types.
The technical exploitation of this vulnerability occurs through crafted DNS responses that contain duplicate CNAME records within signed zones. When Unbound processes these malformed responses, its internal memory management system attempts to deallocate memory that was either never allocated or has already been freed, resulting in a segmentation fault or memory corruption. This memory management error directly violates fundamental security principles outlined in CWE-415, which addresses improper handling of memory allocation and deallocation operations. The vulnerability demonstrates a classic case of double-free errors in memory management where the resolver's code path fails to properly track allocated memory resources during DNS record processing.
From an operational perspective, this vulnerability presents a significant risk for DNS infrastructure as it allows remote attackers to remotely crash the Unbound daemon without requiring any authentication or privileged access. The denial of service impact is severe as it can render DNS resolution services unavailable to legitimate users, potentially causing cascading failures across dependent systems. The attack vector is particularly dangerous because it only requires sending a specially crafted DNS response to a vulnerable Unbound server, making it an attractive target for distributed denial of service attacks. This vulnerability directly maps to ATT&CK technique T1499.004, which covers network denial of service attacks targeting DNS services, and represents a critical weakness in DNS resolver security architecture.
The mitigation strategy for CVE-2011-4528 involves upgrading to Unbound version 1.4.13p2 or later, which includes patches that properly handle memory allocation and deallocation during duplicate CNAME record processing. Organizations should also implement DNS response validation mechanisms and consider deploying DNS security extensions such as DNSSEC to reduce the attack surface. Network administrators should monitor for unusual DNS traffic patterns and implement proper intrusion detection systems to identify potential exploitation attempts. The vulnerability highlights the importance of thorough memory management testing in security-critical software components and demonstrates how seemingly benign DNS record processing can become a vector for system compromise. This issue underscores the necessity of maintaining up-to-date security patches and proper software lifecycle management practices to prevent exploitation of memory corruption vulnerabilities in critical infrastructure components.