CVE-2015-5366 in Linux
Summary
by MITRE
The (1) udp_recvmsg and (2) udpv6_recvmsg functions in the Linux kernel before 4.0.6 provide inappropriate -EAGAIN return values, which allows remote attackers to cause a denial of service (EPOLLET epoll application read outage) via an incorrect checksum in a UDP packet, a different vulnerability than CVE-2015-5364.
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Analysis
by VulDB Data Team • 05/23/2022
The vulnerability identified as CVE-2015-5366 represents a critical flaw in the Linux kernel's UDP network stack implementation that affects versions prior to 4.0.6. This vulnerability specifically impacts the udp_recvmsg and udpv6_recvmsg functions, which are responsible for handling incoming UDP packets in both IPv4 and IPv6 environments. The flaw manifests through improper error handling mechanisms that return incorrect -EAGAIN status codes when processing UDP packets with invalid checksums, creating a significant disruption in network service availability.
The technical root cause of this vulnerability lies in the kernel's network subsystem's handling of UDP packet validation and error propagation. When a UDP packet arrives with an incorrect checksum, the affected kernel functions fail to properly signal the error condition to the epoll event handling system. Instead of returning appropriate error codes that would allow the application to properly handle the malformed packet, the functions return -EAGAIN, which is typically used to indicate that a system call should be retried later. This misclassification causes epoll-based applications to incorrectly interpret the malformed packet as a temporary resource unavailability rather than a legitimate network error condition.
The operational impact of CVE-2015-5366 is severe and manifests as a denial of service condition that specifically affects epoll applications running on vulnerable Linux systems. When remote attackers send UDP packets with incorrect checksums to systems running affected kernel versions, the epoll event loop becomes corrupted and enters a state where it cannot properly process subsequent legitimate network traffic. This creates what is known as an EPOLLET epoll application read outage, where applications that rely on epoll for efficient I/O multiplexing become unresponsive to network events. The vulnerability is particularly dangerous because it can be exploited remotely without authentication, making it a significant threat to network services that depend on epoll-based event handling for their operation.
This vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and demonstrates how network protocol handling flaws can lead to denial of service conditions. The ATT&CK framework categorizes this as a privilege escalation and denial of service technique, as it allows attackers to disrupt system services through network-based attacks. The flaw represents a classic case of improper error handling in kernel space, where the distinction between temporary resource unavailability and permanent protocol errors becomes blurred, leading to cascading failures in network application behavior. Organizations running vulnerable kernel versions face the risk of complete network service disruption, particularly affecting applications such as web servers, database systems, and other network services that rely heavily on epoll for efficient connection handling.
The recommended mitigation strategy involves upgrading to Linux kernel version 4.0.6 or later, where the improper -EAGAIN return values have been corrected. System administrators should also implement network-level filtering to drop UDP packets with invalid checksums where possible, though this approach provides only partial protection. Additionally, monitoring systems should be configured to detect unusual patterns in epoll behavior that might indicate exploitation attempts. Organizations should conduct thorough vulnerability assessments to identify applications that rely on epoll functionality and ensure proper patch management procedures are in place to address this and similar kernel-level network vulnerabilities.