CVE-2016-3707 in Linux
Summary
by MITRE
The icmp_check_sysrq function in net/ipv4/icmp.c in the kernel.org projects/rt patches for the Linux kernel, as used in the kernel-rt package before 3.10.0-327.22.1 in Red Hat Enterprise Linux for Real Time 7 and other products, allows remote attackers to execute SysRq commands via crafted ICMP Echo Request packets, as demonstrated by a brute-force attack to discover a cookie, or an attack that occurs after reading the local icmp_echo_sysrq file.
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Analysis
by VulDB Data Team • 08/25/2022
The vulnerability identified as CVE-2016-3707 represents a critical security flaw in the Linux kernel's handling of ICMP echo requests within the real-time kernel patches. This vulnerability specifically affects the icmp_check_sysrq function located in the net/ipv4/icmp.c file, which governs how the kernel processes certain system request commands through internet control message protocol packets. The issue stems from insufficient validation mechanisms that allow remote attackers to exploit the system's response to crafted ICMP Echo Request packets, effectively bypassing normal security boundaries and enabling unauthorized execution of system commands.
The technical implementation of this vulnerability exploits the kernel's SysRq (System Request) functionality, which provides direct access to kernel-level operations typically restricted to local system administrators. When the kernel receives ICMP Echo Request packets, it processes them through the icmp_check_sysrq function without adequate verification of packet authenticity or source legitimacy. This flaw creates a pathway for attackers to execute SysRq commands remotely, potentially leading to system compromise, privilege escalation, or denial of service conditions. The vulnerability is particularly concerning because it can be exploited through brute-force attacks that systematically test different cookie values, or through more sophisticated methods that leverage reading specific kernel files to gain knowledge of system internals.
From an operational impact perspective, this vulnerability represents a severe threat to Linux-based systems, particularly those running real-time kernel configurations such as Red Hat Enterprise Linux for Real Time 7. Attackers can leverage this flaw to execute arbitrary commands with kernel-level privileges, potentially allowing them to modify system behavior, access sensitive data, or establish persistent backdoors. The vulnerability's exploitability is enhanced by the fact that it requires minimal network access and can be executed remotely, making it particularly dangerous in networked environments where system administrators may not have full control over incoming ICMP traffic. The impact extends beyond individual systems to potentially affect entire network infrastructures, especially in environments where real-time processing requirements make kernel-level access particularly valuable for attackers.
The security implications of CVE-2016-3707 align with CWE-20, which describes improper input validation, and can be mapped to ATT&CK techniques involving privilege escalation and command execution through kernel-level interfaces. Organizations running affected systems face significant risks, as the vulnerability essentially provides an attack surface that bypasses traditional network security controls. The recommended mitigations include applying the vendor-provided patches that address the specific validation issues in the icmp_check_sysrq function, disabling unnecessary ICMP processing where possible, and implementing network-level controls to filter or block suspicious ICMP traffic. System administrators should also consider monitoring for anomalous SysRq command execution patterns and implementing comprehensive logging of kernel-level activities to detect potential exploitation attempts. The vulnerability underscores the importance of maintaining up-to-date kernel versions and proper security configuration management, particularly in real-time systems where kernel-level access can significantly impact system reliability and security posture.