CVE-2015-6125 in Windows
Summary
by MITRE
Use-after-free vulnerability in the DNS server in Microsoft Windows Server 2008 SP2 and R2 SP1 and Server 2012 Gold and R2 allows remote attackers to execute arbitrary code via crafted requests, aka "Windows DNS Use After Free Vulnerability."
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Analysis
by VulDB Data Team • 11/18/2024
The vulnerability identified as CVE-2015-6125 represents a critical use-after-free flaw in Microsoft Windows Server's DNS server implementation affecting Windows Server 2008 SP2 and R2 SP1, as well as Server 2012 Gold and R2. This vulnerability resides within the DNS server component that handles incoming DNS queries and responses, making it a prime target for remote exploitation. The flaw manifests when the DNS server processes malformed or specially crafted DNS requests that trigger improper memory management operations. According to CWE-416, this vulnerability specifically falls under use-after-free conditions where memory allocated to DNS processing structures is freed but subsequently accessed by malicious code, creating a dangerous state where attackers can manipulate the freed memory to execute arbitrary code. The attack vector is entirely remote, requiring no local access or authentication, which significantly expands the potential threat surface. The vulnerability operates through the DNS server's handling of certain record types and query formats that cause the server to allocate memory for processing DNS responses and then free that memory without proper validation before subsequent access attempts.
The technical exploitation of this vulnerability follows a precise sequence that leverages the fundamental memory management flaw in the Windows DNS server implementation. Attackers craft specially formatted DNS requests that trigger the server to allocate memory for processing DNS records, particularly those involving certain resource record types that are processed through vulnerable code paths. When the DNS server processes these malformed requests, it allocates memory structures to handle the response data, but subsequent processing logic causes these structures to be freed prematurely. However, the memory management code does not properly validate that all references to these freed structures have been cleared, allowing attackers to manipulate the freed memory locations to redirect execution flow. This exploitation technique aligns with the attack pattern described in the MITRE ATT&CK framework under T1203 - Exploitation for Client Execution, where adversaries leverage memory corruption vulnerabilities to execute arbitrary code on target systems. The vulnerability's impact extends beyond simple code execution as it provides attackers with a foothold to escalate privileges and potentially compromise the entire DNS infrastructure.
The operational impact of CVE-2015-6125 is severe and multifaceted, particularly for enterprise environments that rely heavily on DNS infrastructure for network operations and security controls. When successfully exploited, this vulnerability allows remote code execution with the privileges of the DNS server process, which typically runs with high privileges on Windows domain controllers and DNS servers. This creates a significant risk for domain-wide compromise, as DNS servers often serve as critical infrastructure components that are difficult to isolate from other network services. The vulnerability can be exploited to establish persistent backdoors, exfiltrate sensitive DNS records, or disrupt critical network services by causing the DNS server to crash or behave unpredictably. Organizations running affected Windows Server versions face potential data breaches, service disruptions, and loss of network control. The vulnerability's presence in Windows Server 2008 and 2012 platforms also means that many legacy systems in enterprise environments remain at risk, particularly those that have not been properly updated or patched. The exploitation can be automated and requires minimal skill, making it attractive to both nation-state actors and common threat actors, which further amplifies the operational risk. Security teams must consider this vulnerability as a potential entry point for broader attacks targeting Active Directory services and network infrastructure.
Mitigation strategies for CVE-2015-6125 should include immediate patch application as the primary defense mechanism, with Microsoft releasing security updates that address the memory management flaw in the DNS server implementation. Organizations should implement network segmentation and access controls to limit exposure of DNS servers to untrusted networks, particularly by restricting DNS query access from external sources. Network monitoring should be enhanced to detect unusual DNS traffic patterns that might indicate exploitation attempts, including malformed DNS queries or unexpected response sizes that could indicate memory corruption attempts. The implementation of DNS server hardening measures such as disabling unnecessary DNS record types, implementing DNS query logging, and deploying intrusion detection systems specifically configured to monitor DNS traffic can provide additional layers of defense. Organizations should also consider implementing DNS cache poisoning detection mechanisms and regular security assessments of their DNS infrastructure to identify potential exploitation indicators. According to industry best practices and security frameworks, implementing these mitigations aligns with the principle of defense in depth, ensuring that even if one layer of protection fails, additional controls remain in place to prevent or detect exploitation attempts. Regular vulnerability assessments and penetration testing should be conducted to verify that the implemented controls effectively mitigate the risk associated with this use-after-free vulnerability.