CVE-2016-0771 in Samba
Summary
by MITRE
The internal DNS server in Samba 4.x before 4.1.23, 4.2.x before 4.2.9, 4.3.x before 4.3.6, and 4.4.x before 4.4.0rc4, when an AD DC is configured, allows remote authenticated users to cause a denial of service (out-of-bounds read) or possibly obtain sensitive information from process memory by uploading a crafted DNS TXT record.
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Analysis
by VulDB Data Team • 07/10/2022
The vulnerability identified as CVE-2016-0771 represents a critical security flaw in Samba's implementation of Active Directory Domain Controller functionality, specifically affecting the internal DNS server component. This issue manifests as an out-of-bounds read condition that can be exploited by authenticated remote attackers who possess valid credentials within the domain environment. The vulnerability impacts multiple versions of Samba 4.x series, creating a widespread risk across various deployment scenarios where Active Directory Domain Controller services are configured. The flaw occurs within the DNS server processing logic when handling specially crafted DNS TXT records, which can trigger memory access violations and potentially expose sensitive data from process memory.
The technical root cause of this vulnerability stems from inadequate input validation within the DNS record processing module of Samba's AD DC implementation. When a malicious user uploads a crafted DNS TXT record, the internal DNS server fails to properly validate the record structure and content before attempting to parse and process it. This insufficient validation leads to memory access beyond the allocated buffer boundaries, resulting in either a denial of service condition where the DNS server crashes or, in some cases, information disclosure through memory dumps. The vulnerability is particularly concerning because it requires only authenticated access within the domain, meaning that an attacker with valid domain credentials can exploit this flaw without requiring additional privileges or network-level access. This characteristic aligns with CWE-129, which describes improper validation of array indices, and demonstrates how insufficient input validation can lead to memory corruption vulnerabilities.
The operational impact of CVE-2016-0771 extends beyond simple service disruption to potentially compromise the confidentiality and integrity of domain services. When the DNS server experiences an out-of-bounds read condition, it can result in system crashes that disrupt critical domain services such as Kerberos authentication, LDAP queries, and other directory services that depend on the DNS infrastructure. The potential for information disclosure adds another layer of risk, as attackers could extract sensitive data from memory locations including cached authentication tokens, session information, or other process-specific data. This vulnerability particularly affects enterprise environments where Samba AD DC implementations are common, potentially undermining the security posture of organizations that rely on these services for authentication and directory management. The attack vector through DNS TXT record uploads follows the pattern of DNS-based attacks that are categorized under ATT&CK technique T1071.004 for application layer protocol: DNS, and demonstrates how DNS services can be leveraged as attack vectors for both denial of service and information gathering purposes.
Organizations affected by this vulnerability should implement immediate mitigations including applying the available patches from Samba releases 4.1.23, 4.2.9, 4.3.6, and 4.4.0rc4 respectively. The most effective immediate solution involves upgrading to patched versions of Samba that contain proper input validation for DNS record processing. Network segmentation and access controls should be reviewed to limit the scope of potential exploitation by restricting access to DNS record upload capabilities to only trusted administrative users. Monitoring should be enhanced to detect unusual DNS TXT record uploads and potential exploitation attempts. The vulnerability also highlights the importance of proper input validation in DNS server implementations and reinforces the need for comprehensive security testing of directory services. Organizations should conduct vulnerability assessments to identify all instances of Samba AD DC deployments and ensure that all systems are updated to patched versions. Additionally, implementing network-based intrusion detection systems that can monitor for DNS-based attack patterns and establishing incident response procedures for handling DNS-related security incidents will help mitigate the overall risk associated with this vulnerability. The remediation process should also include reviewing and hardening DNS server configurations to reduce the attack surface and implementing proper access controls for DNS record management functions.