CVE-2016-8666 in Linux
Summary
by MITRE • 01/25/2023
The IP stack in the Linux kernel before 4.6 allows remote attackers to cause a denial of service (stack consumption and panic) or possibly have unspecified other impact by triggering use of the GRO path for packets with tunnel stacking, as demonstrated by interleaved IPv4 headers and GRE headers, a related issue to CVE-2016-7039.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2016-8666 represents a critical flaw in the Linux kernel's network stack implementation that affects versions prior to 4.6. This issue specifically targets the Generic Receive Offload (GRO) functionality, which is designed to improve network performance by aggregating multiple small packets into larger ones before processing. The vulnerability arises when the kernel encounters packets that utilize tunnel stacking techniques, particularly those with interleaved IPv4 headers and GRE (Generic Routing Encapsulation) headers, creating a scenario where the network stack becomes overwhelmed during packet processing.
The technical exploitation of this vulnerability occurs through the manipulation of network packet structures that trigger the GRO path in an unexpected manner. When the kernel receives packets with stacked tunnel headers, the processing logic becomes susceptible to stack consumption issues that can lead to system instability. The flaw specifically leverages the interaction between different header types within the network protocol stack, where the GRO mechanism attempts to aggregate packets that have been constructed with nested encapsulation layers. This creates a condition where the kernel's internal data structures become exhausted, leading to the denial of service conditions that can either consume system stack resources or trigger kernel panics, effectively rendering the affected system unavailable to legitimate network traffic.
From an operational perspective, this vulnerability poses significant risks to network infrastructure and system availability. The potential for remote exploitation means that attackers can trigger the vulnerability from external networks without requiring local access or authentication. The impact extends beyond simple denial of service to potentially include unspecified other impacts that could compromise system integrity. Network administrators face the challenge of identifying and mitigating this vulnerability across systems that may be processing tunnelled network traffic, particularly in environments that utilize virtual private networks, network virtualization, or other technologies that employ encapsulation mechanisms. The vulnerability's relationship to CVE-2016-7039 demonstrates a broader pattern of issues affecting the Linux kernel's handling of packet aggregation and tunneling scenarios, indicating systemic weaknesses in the network stack's robustness.
The mitigation strategies for CVE-2016-8666 primarily involve upgrading to Linux kernel version 4.6 or later, where the vulnerability has been addressed through patches that improve the handling of tunnel stacking scenarios within the GRO mechanism. Organizations should also implement network monitoring to detect unusual packet patterns that might indicate exploitation attempts, and consider implementing network segmentation to limit the potential impact of such attacks. The vulnerability aligns with CWE-129, which addresses issues related to improper handling of input data, and relates to ATT&CK technique T1499.004 for network denial of service attacks. Security teams should prioritize patch management for this vulnerability due to its remote exploitability and potential for system instability, particularly in environments where network virtualization or tunneling technologies are extensively used. The remediation process requires careful consideration of system compatibility and potential performance impacts from the kernel updates, as well as thorough testing to ensure that legitimate network operations continue to function properly after the patches are applied.