CVE-2019-15919 in Linux
Summary
by MITRE
An issue was discovered in the Linux kernel before 5.0.10. SMB2_write in fs/cifs/smb2pdu.c has a use-after-free.
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Analysis
by VulDB Data Team • 12/13/2023
The vulnerability identified as CVE-2019-15919 represents a critical use-after-free flaw within the Linux kernel's SMB2 implementation, specifically affecting versions prior to 5.0.10. This issue resides in the fs/cifs/smb2pdu.c file where the SMB2_write function fails to properly manage memory references, creating a scenario where freed memory locations can be accessed or reused by subsequent operations. The vulnerability manifests during SMB2 protocol operations involving file write requests, making it particularly dangerous in networked environments where SMB services are actively utilized.
The technical nature of this flaw stems from improper memory management practices within the kernel's SMB2 subsystem, where data structures allocated for handling write operations are freed before all references to them are properly cleared or validated. This creates a window of opportunity for malicious actors to exploit the dangling pointer, potentially leading to arbitrary code execution or system compromise. The use-after-free condition occurs when the kernel attempts to access memory that has already been deallocated, violating fundamental memory safety principles and creating potential attack vectors for privilege escalation.
From an operational perspective, this vulnerability poses significant risks to Linux systems that implement SMB2 file sharing services, particularly those running kernel versions below 5.0.10. Attackers could leverage this flaw by crafting malicious SMB2 write requests that trigger the use-after-free condition, potentially allowing them to execute arbitrary code with kernel privileges. The impact extends beyond simple system compromise, as this vulnerability could enable attackers to establish persistent backdoors, escalate privileges, or cause system instability through controlled memory corruption. Organizations using Linux servers for file sharing, particularly those with SMB services enabled, face heightened security risks due to the potential for remote code execution.
The vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software implementations, and represents a classic example of memory safety issues that can be exploited for privilege escalation attacks. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and code execution within kernel space, potentially enabling adversaries to bypass standard user-level security controls. The exploitation of this flaw would typically involve crafting specific SMB2 protocol requests that cause the kernel to free memory structures while maintaining references to them, creating opportunities for memory corruption that could be leveraged for malicious purposes.
Organizations should prioritize immediate patching of affected systems to address this vulnerability, ensuring kernel versions are updated to 5.0.10 or later where the memory management issues have been resolved. System administrators should implement network segmentation to limit SMB service exposure and monitor for suspicious SMB2 traffic patterns that might indicate exploitation attempts. Additionally, deploying intrusion detection systems capable of identifying anomalous SMB2 protocol behavior can help detect potential exploitation attempts. The remediation process should include comprehensive testing of updated kernels to ensure compatibility with existing SMB services while maintaining security posture against this and related memory safety vulnerabilities.