CVE-2014-0239 in Samba
Summary
by MITRE
The internal DNS server in Samba 4.x before 4.0.18 does not check the QR field in the header section of an incoming DNS message before sending a response, which allows remote attackers to cause a denial of service (CPU and bandwidth consumption) via a forged response packet that triggers a communication loop, a related issue to CVE-1999-0103.
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Analysis
by VulDB Data Team • 06/20/2021
The vulnerability described in CVE-2014-0239 represents a critical flaw in the Samba 4.x DNS server implementation that undermines the integrity of network communications and system availability. This issue affects Samba versions prior to 4.0.18 and specifically targets the internal DNS server component that handles incoming DNS queries and responses. The flaw stems from insufficient validation of DNS message headers, creating a pathway for malicious actors to exploit the system through carefully crafted forged packets that manipulate the QR (Query/Response) field in the DNS header section.
The technical implementation of this vulnerability occurs when the Samba DNS server fails to verify the QR field in incoming DNS messages before processing and responding to them. In standard DNS operations, the QR field indicates whether a message is a query (0) or a response (1), serving as a fundamental protocol element for proper message handling. When this field is not validated, the server can be tricked into treating incoming response packets as if they were queries, leading to a cascading effect where the server continuously processes and retransmits these malformed messages. This communication loop consumes significant CPU resources and network bandwidth, effectively creating a denial of service condition that can overwhelm the system and render it unavailable to legitimate users.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader network stability concerns and resource exhaustion. Attackers can leverage this flaw to create sustained denial of service conditions that consume system resources at a rate that can degrade performance or completely incapacitate the affected Samba server. The vulnerability's relationship to CVE-1999-0103 demonstrates a pattern of DNS-related flaws that exploit fundamental protocol implementations, with this particular issue representing a regression or oversight in the Samba 4.x implementation. The resource consumption characteristics make this attack particularly effective as a low-bandwidth, high-impact method for system disruption.
This vulnerability aligns with several cybersecurity frameworks and threat modeling approaches, including CWE-254 which addresses weaknesses in authentication and access control, and relates to ATT&CK technique T1498 for network denial of service attacks. The flaw demonstrates poor input validation practices that violate fundamental security principles, and the lack of proper header field verification represents a failure in protocol compliance. Organizations implementing Samba DNS services should prioritize immediate patching to address this vulnerability, as the attack vector requires minimal sophistication while delivering significant impact. The remediation approach involves updating to Samba 4.0.18 or later versions where the DNS header validation has been properly implemented, along with implementing network monitoring to detect anomalous DNS traffic patterns that may indicate exploitation attempts.