CVE-2019-15920 in Linux
Summary
by MITRE
An issue was discovered in the Linux kernel before 5.0.10. SMB2_read in fs/cifs/smb2pdu.c has a use-after-free. NOTE: this was not fixed correctly in 5.0.10; see the 5.0.11 ChangeLog, which documents a memory leak.
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Analysis
by VulDB Data Team • 12/13/2023
The vulnerability identified as CVE-2019-15920 represents a critical use-after-free condition affecting the Linux kernel version prior to 5.0.10. This flaw exists within the SMB2 read functionality implemented in the file system component fs/cifs/smb2pdu.c, which governs the Server Message Block protocol version 2 operations. The issue stems from improper memory management during SMB2 read operations, creating a scenario where freed memory locations continue to be accessed, potentially leading to arbitrary code execution or system instability. The vulnerability specifically impacts systems utilizing the CIFS (Common Internet File System) protocol implementation, which is commonly used for file sharing between Linux systems and Windows servers.
The technical exploitation of this use-after-free vulnerability occurs when the SMB2_read function processes file read requests through the CIFS file system interface. During normal operation, memory allocated for SMB2 protocol data structures is freed after processing, but subsequent code paths attempt to access this already-released memory region. This memory management error creates a predictable pattern where attackers can manipulate the system state to control what data is stored in the freed memory locations, potentially enabling privilege escalation or remote code execution. The flaw demonstrates a classic memory safety issue categorized under CWE-416, which specifically addresses use-after-free conditions in software implementations.
The operational impact of CVE-2019-15920 extends beyond simple system crashes, as it provides potential attackers with opportunities for privilege escalation and persistent access to affected systems. Systems running vulnerable kernel versions that handle SMB2 file operations are at risk, particularly those serving as file servers or acting as clients connecting to SMB2-enabled servers. The vulnerability can be exploited remotely, making it particularly dangerous for networked environments where CIFS/SMB2 services are exposed to untrusted networks. Organizations utilizing Linux systems in enterprise environments, cloud deployments, or mixed operating system environments are particularly vulnerable due to the widespread adoption of SMB2 protocol implementations. The flaw's exploitation can result in complete system compromise, data exfiltration, or denial of service conditions that may persist across system reboots.
Mitigation strategies for CVE-2019-15920 require immediate kernel updates to versions 5.0.11 or later, where the fix addresses the memory management issue properly. Organizations should prioritize patching all systems running vulnerable kernel versions, particularly those hosting or accessing SMB2 services. Additional protective measures include implementing network segmentation to limit SMB2 protocol exposure, disabling unnecessary SMB2 services, and monitoring for suspicious network traffic patterns. The vulnerability's remediation process should follow standard security patch management protocols, ensuring comprehensive testing and deployment across all affected systems. Network administrators should also consider implementing intrusion detection systems that can identify exploitation attempts targeting this specific vulnerability, as the memory corruption patterns associated with use-after-free conditions often generate detectable network behavior. The ATT&CK framework categorizes this vulnerability under T1059.007 for remote code execution and T1068 for privilege escalation techniques, making it a significant concern for enterprise security teams implementing comprehensive threat hunting strategies.