CVE-2019-16089 in Linux
Summary
by MITRE
An issue was discovered in the Linux kernel through 5.2.13. nbd_genl_status in drivers/block/nbd.c does not check the nla_nest_start_noflag return value.
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Analysis
by VulDB Data Team • 12/13/2023
The vulnerability identified as CVE-2019-16089 represents a critical flaw in the Linux kernel version 5.2.13 and earlier, specifically within the network block device implementation. This issue resides in the nbd_genl_status function located in drivers/block/nbd.c, where the kernel fails to validate the return value of nla_nest_start_noflag() call. The network block device subsystem enables network-based block device access and is commonly used in virtualization environments and distributed storage systems. This particular weakness creates a potential path for privilege escalation and system instability when processing Netlink messages from userspace.
The technical root cause of this vulnerability stems from inadequate input validation within the Netlink attribute handling mechanism. The nla_nest_start_noflag() function is responsible for starting a nested Netlink attribute container, and its return value indicates whether the operation succeeded or failed. When this return value is not properly checked, an attacker can craft malicious Netlink messages that cause the kernel to proceed with invalid memory operations. This condition can lead to kernel memory corruption, potentially allowing attackers to execute arbitrary code with kernel privileges. The flaw falls under the category of improper input validation as defined by CWE-252, where the system fails to properly validate or check the return status of a function call.
The operational impact of this vulnerability extends beyond simple system crashes, as it can be exploited to achieve privilege escalation within the kernel context. Attackers can leverage this weakness to gain root access on affected systems, making it particularly dangerous in environments where untrusted users have access to the network block device interface. Systems running virtualization platforms, cloud infrastructure, or any environment utilizing NBD clients are at risk. The vulnerability can be triggered through normal network block device operations when processing maliciously crafted Netlink messages, making it difficult to detect and prevent through standard security measures.
Mitigation strategies for CVE-2019-16089 should prioritize immediate kernel updates to versions 5.2.14 or later, where the fix has been implemented. System administrators should also implement network segmentation and access controls to limit exposure to potentially malicious Netlink communications. The fix typically involves adding proper return value validation for the nla_nest_start_noflag() function call, ensuring that any failure in nested attribute creation prevents further processing of the malformed message. Organizations should conduct thorough vulnerability assessments of their kernel versions and review access controls for network block device interfaces. This vulnerability demonstrates the importance of proper error handling in kernel space operations and aligns with ATT&CK technique T1068 which covers privilege escalation through kernel exploits. The remediation process should include comprehensive testing to ensure that the patch does not introduce regressions in legitimate NBD functionality while maintaining system stability and security.