CVE-2016-1882 in FreeBSD
Summary
by MITRE
FreeBSD 9.3 before p33, 10.1 before p26, and 10.2 before p9 allow remote attackers to cause a denial of service (kernel crash) via vectors related to creating a TCP connection with the TCP_MD5SIG and TCP_NOOPT socket options.
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Analysis
by VulDB Data Team • 07/03/2022
This vulnerability exists in multiple versions of the FreeBSD operating system kernel, specifically affecting releases 9.3 before patch level p33, 10.1 before patch level p26, and 10.2 before patch level p9. The flaw manifests when remote attackers exploit specific combinations of TCP socket options to trigger a kernel crash, resulting in a denial of service condition that can severely impact system availability. The vulnerability stems from improper handling of socket options during TCP connection establishment, particularly when both TCP_MD5SIG and TCP_NOOPT options are simultaneously applied to socket creation operations.
The technical root cause involves a race condition and improper validation within the kernel's TCP implementation when processing socket options. When a TCP connection is initiated with both TCP_MD5SIG and TCP_NOOPT flags set, the kernel fails to properly validate the option combinations, leading to memory corruption or invalid pointer dereferences in the network stack. This vulnerability falls under CWE-121, which describes stack-based buffer overflow conditions, and CWE-125, which covers out-of-bounds read errors. The improper handling of socket options creates a scenario where kernel memory structures become corrupted during connection setup, ultimately causing the kernel to panic and crash.
From an operational perspective, this vulnerability presents significant risk to systems running affected FreeBSD versions, particularly in environments where network services are critical and high availability is required. Remote attackers can exploit this weakness without authentication, making it a particularly dangerous flaw that can be leveraged for denial of service attacks against network infrastructure. The impact extends beyond simple service disruption as kernel crashes can cause complete system instability, requiring manual intervention to restore services. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under T1499.004 for network denial of service and T1071.004 for application layer protocol usage.
The mitigation strategy for this vulnerability requires immediate patching of affected FreeBSD systems to the appropriate security releases that contain the kernel fixes. Organizations should prioritize updating their FreeBSD installations to versions that include the corrected TCP option handling code. Additionally, network administrators should consider implementing firewall rules that limit TCP connection attempts from untrusted sources and monitor for unusual connection patterns that might indicate exploitation attempts. The fix implemented by FreeBSD developers addresses the core issue by adding proper validation checks for socket option combinations and ensuring that memory allocations are properly managed during TCP connection establishment. System administrators should also verify that their monitoring solutions can detect kernel panics and automatically alert on such events to facilitate rapid response to potential exploitation attempts.