CVE-2015-1573 in Linux
Summary
by MITRE
The nft_flush_table function in net/netfilter/nf_tables_api.c in the Linux kernel before 3.18.5 mishandles the interaction between cross-chain jumps and ruleset flushes, which allows local users to cause a denial of service (panic) by leveraging the CAP_NET_ADMIN capability.
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Analysis
by VulDB Data Team • 03/09/2022
The vulnerability identified as CVE-2015-1573 resides within the Linux kernel's netfilter subsystem, specifically in the nft_flush_table function located in net/netfilter/nf_tables_api.c. This flaw represents a critical denial of service vulnerability that affects Linux kernel versions prior to 3.18.5, demonstrating a fundamental issue in how the kernel handles rule set operations and chain management. The vulnerability exploits a race condition between cross-chain jumps and ruleset flush operations, creating a scenario where malicious local users with the CAP_NET_ADMIN capability can trigger a kernel panic.
The technical root cause of this vulnerability stems from improper handling of reference counting and chain state management during flush operations. When the nft_flush_table function processes a ruleset flush, it fails to properly account for cross-chain jump references that may still exist within the system. This improper state management creates a scenario where freed memory structures can be accessed or modified after deallocation, leading to kernel memory corruption. The vulnerability specifically manifests when multiple chains reference each other through jump statements and a flush operation occurs simultaneously, causing the kernel's nf_tables subsystem to enter an inconsistent state that ultimately results in a system panic.
The operational impact of CVE-2015-1573 extends beyond simple denial of service, as it can be exploited by local users with network administration privileges to disrupt system availability. This vulnerability is particularly concerning because it requires only the CAP_NET_ADMIN capability, which is commonly granted to network administrators and certain system services. Attackers can leverage this privilege to execute a denial of service attack that brings the entire system to a halt, potentially affecting critical infrastructure services. The vulnerability's exploitation is straightforward and reliable, making it an attractive target for malicious actors seeking to disrupt system operations without requiring elevated privileges beyond what is typically available to network administrators.
From a cybersecurity perspective, this vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and represents a classic case of improper resource management in kernel space. The ATT&CK framework categorizes this as a privilege escalation technique through local system exploitation, where the initial access vector is through legitimate administrative capabilities. The vulnerability demonstrates the importance of proper synchronization mechanisms in kernel-level code and highlights the risks associated with complex inter-chain relationships in packet filtering systems. Organizations should prioritize patching this vulnerability as it represents a straightforward path to system disruption that can be exploited by both malicious insiders and external attackers who have gained access to network administration credentials.
Mitigation strategies for CVE-2015-1573 primarily involve upgrading to Linux kernel versions 3.18.5 or later, where the vulnerability has been addressed through proper reference counting and chain state management. System administrators should also implement strict access controls to limit who possesses the CAP_NET_ADMIN capability, as this privilege is essential for exploiting the vulnerability. Monitoring for unusual network administration activities and implementing robust system logging can help detect potential exploitation attempts. Additionally, organizations should consider implementing network segmentation and access control measures to limit the potential impact of such vulnerabilities, particularly in environments where multiple administrators have elevated privileges. The fix implemented in kernel 3.18.5 involves proper handling of cross-chain references during flush operations, ensuring that all references are properly accounted for before memory deallocation occurs.