CVE-2020-25645 in Linux
Summary
by MITRE • 10/14/2020
A flaw was found in the Linux kernel in versions before 5.9-rc7. Traffic between two Geneve endpoints may be unencrypted when IPsec is configured to encrypt traffic for the specific UDP port used by the GENEVE tunnel allowing anyone between the two endpoints to read the traffic unencrypted. The main threat from this vulnerability is to data confidentiality.
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Analysis
by VulDB Data Team • 11/19/2020
The vulnerability described in CVE-2020-25645 represents a critical weakness in the Linux kernel's handling of Geneve tunneling protocols within IPsec encryption contexts. This flaw exists in kernel versions prior to 5.9-rc7 and specifically affects the encryption of traffic between Geneve endpoints. Geneve tunneling protocol operates at the network layer and uses UDP port numbers to establish communication channels between tunnel endpoints. When IPsec is configured to encrypt traffic for specific UDP ports, the vulnerability allows attackers positioned between the two Geneve endpoints to intercept and read traffic that should remain encrypted. The issue stems from improper handling of the Geneve protocol within the kernel's IPsec implementation, creating a decryption bypass that undermines the fundamental security assurances provided by IPsec encryption.
The technical implementation of this vulnerability involves the Linux kernel's network stack failing to properly enforce encryption policies when Geneve tunnels are established alongside IPsec configurations. Specifically, when IPsec is configured to encrypt traffic for a particular UDP port, the kernel does not adequately validate that all traffic flowing through that port is indeed encrypted. This creates a scenario where Geneve traffic can flow unencrypted even when the system is configured to encrypt all traffic for that port. The flaw operates at the intersection of the Geneve tunneling protocol implementation and the IPsec security policy enforcement mechanisms, where the kernel's security boundaries are not properly maintained. This represents a classic case of insufficient input validation and policy enforcement within kernel networking code, aligning with CWE-284 Access Control Issues and CWE-310 Cryptographic Issues.
The operational impact of CVE-2020-25645 is significant for any organization relying on IPsec-encrypted Geneve tunnels for network security. Data confidentiality is the primary concern, as attackers can intercept and read sensitive information flowing between Geneve endpoints without detection. This vulnerability particularly affects network infrastructure deployments using Geneve for overlay networking, such as software-defined networking environments, container networking solutions, and virtualized network deployments. The threat is especially concerning because it operates at the network layer where traffic flows are typically expected to be secure, and the encryption bypass occurs transparently without any indication to the network administrators or applications. This vulnerability can be exploited by man-in-the-middle attackers positioned anywhere along the communication path between Geneve endpoints, potentially exposing sensitive data including authentication credentials, application data, and system information.
Mitigation strategies for CVE-2020-25645 primarily involve upgrading to Linux kernel versions 5.9-rc7 or later where the vulnerability has been addressed. Organizations should prioritize kernel updates across their network infrastructure, particularly in environments using Geneve tunneling protocols with IPsec encryption. Additionally, network administrators can implement temporary workarounds such as disabling Geneve tunneling when IPsec encryption is required, or using alternative tunneling protocols that do not exhibit this behavior. Security monitoring should be enhanced to detect unusual traffic patterns that might indicate exploitation attempts, and network segmentation strategies can help limit the potential impact if the vulnerability is exploited. The fix implemented in kernel versions 5.9-rc7 addresses the core issue by ensuring proper policy enforcement between Geneve protocol handling and IPsec encryption mechanisms, preventing the bypass that allowed unencrypted traffic flow. This vulnerability demonstrates the importance of thorough protocol integration testing in kernel security implementations and aligns with ATT&CK technique T1041 Network Sniffing and T1566 Phishing as it represents a network-level data exposure that can be exploited by attackers with network access.