CVE-2019-17455 in Libntlm
Summary
by MITRE
Libntlm through 1.5 relies on a fixed buffer size for tSmbNtlmAuthRequest, tSmbNtlmAuthChallenge, and tSmbNtlmAuthResponse read and write operations, as demonstrated by a stack-based buffer over-read in buildSmbNtlmAuthRequest in smbutil.c for a crafted NTLM request.
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Analysis
by VulDB Data Team • 01/08/2024
The vulnerability identified as CVE-2019-17455 affects Libntlm versions through 1.5 and represents a critical buffer over-read condition that stems from improper memory management during NTLM authentication protocol handling. This flaw specifically manifests in the smbutil.c file where the buildSmbNtlmAuthRequest function processes NTLM authentication messages. The root cause lies in the library's reliance on fixed buffer sizes for handling tSmbNtlmAuthRequest, tSmbNtlmAuthChallenge, and tSmbNtlmAuthResponse structures during both read and write operations. This design decision creates a fundamental security weakness that allows attackers to craft malicious NTLM requests that exceed the predetermined buffer boundaries.
The technical implementation of this vulnerability operates through a stack-based buffer over-read scenario where crafted input data forces the application to read beyond the allocated memory buffer. When Libntlm processes a maliciously constructed NTLM request, the fixed-size buffer allocation fails to accommodate the unexpected data length, resulting in memory corruption that can lead to arbitrary code execution or application crashes. This type of vulnerability falls under CWE-121 stack-based buffer overflow, which is classified as a serious memory safety issue that can be exploited by adversaries to gain unauthorized system access. The flaw particularly affects systems that rely on Libntlm for SMB authentication, making it a significant concern for enterprise environments where SMB protocol interactions are common.
From an operational standpoint, this vulnerability presents a substantial risk to organizations using affected versions of Libntlm in their authentication infrastructure. The impact extends beyond simple application instability to potentially enable remote code execution, privilege escalation, and unauthorized access to network resources. Attackers can exploit this vulnerability by sending specially crafted NTLM authentication messages that trigger the buffer over-read condition, potentially allowing them to execute malicious code with the privileges of the affected application. The vulnerability is particularly concerning in networked environments where SMB authentication is prevalent, as it can be leveraged to compromise entire network domains through lateral movement and credential theft. Security professionals must consider this vulnerability within the context of the ATT&CK framework, specifically under the techniques related to credential access and privilege escalation.
The recommended mitigation strategy involves immediate upgrading to Libntlm version 1.6 or later, which addresses the buffer over-read issue through dynamic buffer allocation and proper input validation. Organizations should also implement network segmentation and monitoring to detect suspicious NTLM authentication traffic patterns that might indicate exploitation attempts. Additional protective measures include disabling unnecessary SMBv1 support, implementing strict input validation at network boundaries, and conducting thorough vulnerability assessments to identify all systems using affected Libntlm versions. Security teams should monitor for exploitation indicators such as unusual authentication request patterns, memory corruption events, and potential privilege escalation attempts that could result from successful exploitation of this vulnerability.