CVE-2023-38427 in Linux
Summary
by MITRE • 07/18/2023
An issue was discovered in the Linux kernel before 6.3.8. fs/smb/server/smb2pdu.c in ksmbd has an integer underflow and out-of-bounds read in deassemble_neg_contexts.
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Analysis
by VulDB Data Team • 01/19/2026
The vulnerability identified as CVE-2023-38427 represents a critical security flaw within the Linux kernel's ksmbd implementation that affects systems running kernel versions prior to 6.3.8. This issue resides in the file fs/smb/server/smb2pdu.c and specifically targets the deassemble_neg_contexts function which processes SMB2 negotiation contexts. The vulnerability manifests as an integer underflow followed by an out-of-bounds read operation that occurs when processing certain SMB2 protocol negotiations. This flaw is particularly concerning because it exists within the core SMB server implementation that handles network file sharing operations, making it a prime target for remote exploitation in networked environments where SMB services are active.
The technical execution of this vulnerability involves a specific sequence of operations that begins with an integer underflow condition in the context processing logic. When the ksmbd server receives an SMB2 negotiation request containing specially crafted context data, the integer underflow causes a negative value to be used as an array index or buffer size parameter. This negative value then propagates into a subsequent memory access operation that results in an out-of-bounds read. The underlying mechanism operates through improper input validation where the length field of SMB2 negotiation contexts is not adequately checked against expected boundaries before being used in memory operations. This type of vulnerability falls under CWE-191 Integer Underflow (Wrap or Wraparound) and CWE-129 Improper Validation of Array Index, both of which are classified as high-risk issues in the Common Weakness Enumeration catalog. The vulnerability can be exploited by remote attackers who send malicious SMB2 negotiation packets to systems running vulnerable kernel versions.
The operational impact of CVE-2023-38427 extends beyond simple memory corruption as it can potentially lead to arbitrary code execution, information disclosure, or system instability. When the out-of-bounds read occurs, it may allow attackers to read sensitive kernel memory contents, potentially exposing credentials, cryptographic keys, or other confidential information stored in memory. The integer underflow condition can also cause the system to behave unpredictably, leading to denial of service conditions that can disrupt SMB services and potentially affect other network operations. This vulnerability is particularly dangerous in enterprise environments where SMB services are commonly used for file sharing, printer services, and other network operations. The attack vector requires network access to the affected system and does not require authentication for exploitation, making it a significant threat in unsecured network environments where SMB services are exposed to external traffic.
Mitigation strategies for this vulnerability should prioritize immediate kernel updates to versions 6.3.8 or later where the issue has been patched. Organizations should conduct comprehensive vulnerability assessments to identify all systems running affected kernel versions and prioritize patching of critical infrastructure components. Network segmentation and access control measures should be implemented to limit exposure of SMB services to trusted networks only, reducing the attack surface for remote exploitation attempts. The patch addresses the vulnerability by implementing proper bounds checking on integer values used in context processing operations and ensuring that all input parameters are validated before being used in memory operations. Security monitoring should be enhanced to detect unusual SMB2 negotiation patterns that might indicate exploitation attempts, and system administrators should implement regular security audits to verify that all systems remain patched against known vulnerabilities. This vulnerability aligns with ATT&CK technique T1071.004 Application Layer Protocol SMB/Windows Admin Shares, which focuses on the exploitation of SMB protocols for lateral movement and privilege escalation within network environments. Organizations should also consider implementing network-based intrusion detection systems that can identify and block suspicious SMB2 protocol traffic patterns associated with this specific vulnerability class.