CVE-2018-6916 in FreeBSD
Summary
by MITRE
In FreeBSD before 11.1-STABLE, 11.1-RELEASE-p7, 10.4-STABLE, 10.4-RELEASE-p7, and 10.3-RELEASE-p28, the kernel does not properly validate IPsec packets coming from a trusted host. Additionally, a use-after-free vulnerability exists in the IPsec AH handling code. This issue could cause a system crash or other unpredictable results.
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Analysis
by VulDB Data Team • 02/21/2023
The vulnerability identified as CVE-2018-6916 represents a critical security flaw in FreeBSD operating systems affecting multiple release versions including 11.1-STABLE through 11.1-RELEASE-p7, 10.4-STABLE through 10.4-RELEASE-p7, and 10.3-RELEASE-p28. This issue resides within the kernel's IPsec packet processing mechanisms and specifically targets the Authentication Header (AH) handling code that is fundamental to secure network communications. The flaw manifests when the kernel fails to properly validate IPsec packets originating from trusted hosts, creating a potential attack vector that could be exploited by malicious actors who have gained access to the trusted network segment.
The technical implementation of this vulnerability involves a use-after-free condition within the IPsec AH processing code, which is classified under CWE-416 as improper cleanup of memory resources. This memory corruption vulnerability occurs when the kernel attempts to access memory that has already been freed during the processing of authenticated IPsec packets. The root cause stems from inadequate input validation mechanisms that fail to properly verify packet integrity and authenticity before processing. When a maliciously crafted IPsec packet is received, the kernel's validation routines are bypassed due to the trusted host assumption, allowing malformed packets to trigger the use-after-free condition that results in memory corruption.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable privilege escalation and remote code execution in certain scenarios. When the use-after-free condition is triggered, it can cause system crashes, kernel panics, and unpredictable behavior that may be exploited to gain unauthorized access to the system. The vulnerability is particularly concerning because it operates under the assumption that hosts within a trusted network segment are inherently secure, which is a common security model in many enterprise environments. This misconfiguration allows attackers to leverage legitimate network connections to execute malicious payloads that could compromise the entire system.
Mitigation strategies for CVE-2018-6916 require immediate system updates to the patched FreeBSD versions that contain the necessary kernel fixes. Organizations should prioritize patching all affected systems, particularly those running IPsec services or relying on IPsec for network security. Network administrators should implement additional monitoring and intrusion detection systems to identify suspicious IPsec traffic patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1071.004 for application layer protocol and T1499.004 for network disruption, making it particularly relevant for security teams implementing defensive measures against both network-based attacks and system compromise scenarios. System administrators should also consider disabling IPsec services when not required and implementing strict network segmentation policies to limit the potential impact of such vulnerabilities.