CVE-2018-6918 in AirPort Base Station
Summary
by MITRE
In FreeBSD before 11.1-STABLE, 11.1-RELEASE-p9, 10.4-STABLE, 10.4-RELEASE-p8 and 10.3-RELEASE-p28, the length field of the ipsec option header does not count the size of the option header itself, causing an infinite loop when the length is zero. This issue can allow a remote attacker who is able to send an arbitrary packet to cause the machine to crash.
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Analysis
by VulDB Data Team • 09/26/2023
The vulnerability described in CVE-2018-6918 represents a critical buffer handling flaw within the FreeBSD operating system's IPsec implementation that affects multiple versions including 11.1-STABLE, 11.1-RELEASE-p9, 10.4-STABLE, 10.4-RELEASE-p8, and 10.3-RELEASE-p28. This issue resides in the processing of IPsec option headers where the length field fails to account for the size of the option header itself, creating a fundamental protocol parsing error that can be exploited remotely. The flaw manifests when an attacker crafts a packet with a zero-length IPsec option header, which causes the kernel's packet processing routine to enter an infinite loop due to improper boundary checking and iteration logic.
The technical nature of this vulnerability stems from a classic buffer overflow condition where the length field in the IPsec option header is interpreted incorrectly by the kernel's network stack. When the length field contains a value of zero, the kernel's processing loop fails to properly terminate its iteration over the option header structure, leading to an infinite loop that consumes CPU resources and eventually causes system crashes. This behavior directly maps to CWE-129, which describes improper validation of length fields, and specifically relates to CWE-772, which addresses missing release of resource after effective lifetime. The vulnerability operates at the kernel level within the network protocol stack, making it particularly dangerous as it can be triggered by any remote entity capable of sending malicious packets to the target system.
The operational impact of CVE-2018-6918 extends beyond simple system crashes to encompass potential denial of service attacks that can render affected FreeBSD systems completely unresponsive. Attackers can exploit this vulnerability without requiring authentication or special privileges, making it particularly dangerous in network environments where untrusted traffic flows through the affected systems. The infinite loop condition causes the kernel to consume excessive CPU cycles, potentially leading to resource exhaustion and system instability that can affect network connectivity, application availability, and overall system performance. This vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a critical weakness in the operating system's input validation mechanisms that could be leveraged in coordinated attack campaigns.
Mitigation strategies for this vulnerability require immediate system updates to the patched versions of FreeBSD that address the incorrect length field handling in IPsec option headers. System administrators should prioritize patching affected systems to prevent exploitation, as the vulnerability can be triggered remotely without authentication. Network administrators can implement additional protective measures such as firewall rules that filter IPsec traffic or disable IPsec functionality if it is not required for operations. The fix typically involves correcting the kernel's packet processing logic to properly account for the size of the option header when validating the length field, ensuring that zero-length headers are handled gracefully without causing infinite loops. Organizations should also consider implementing network monitoring solutions to detect anomalous packet patterns that may indicate exploitation attempts, and establish incident response procedures to address potential system compromises.