CVE-2005-2068 in FreeBSD
Summary
by MITRE
FreeBSD 4.x through 4.11 and 5.x through 5.4 allows remote attackers to modify certain TCP options via a TCP packet with the SYN flag set for an already established session.
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Analysis
by VulDB Data Team • 06/02/2019
The vulnerability described in CVE-2005-2068 represents a significant security flaw in the FreeBSD operating system family affecting versions 4.x through 4.11 and 5.x through 5.4. This issue pertains to the improper handling of TCP options within the network stack, specifically when processing TCP packets that contain the SYN flag set for connections that are already established. The flaw exists in the kernel-level TCP implementation where the system fails to properly validate or reject malformed TCP options in established sessions, creating an avenue for remote attackers to manipulate connection parameters.
The technical nature of this vulnerability stems from the TCP protocol implementation within FreeBSD's networking stack. When a TCP packet with the SYN flag is received for an already established connection, the system should either ignore such packets or properly handle them according to TCP specifications. However, the flaw allows attackers to inject or modify TCP options that are typically only valid during connection establishment phases. This behavior violates fundamental TCP protocol semantics and creates a window for exploitation where malicious actors can alter connection parameters without proper authentication or authorization.
From an operational impact perspective, this vulnerability enables remote attackers to potentially manipulate established TCP sessions, which could lead to various security consequences including session hijacking, connection termination, or modification of data flow characteristics. The attack requires the adversary to be able to send crafted TCP packets to the target system, typically through network interception or by exploiting network topology to position themselves between the client and server. The vulnerability is particularly concerning because it operates at the transport layer, affecting the fundamental reliability and integrity guarantees that TCP provides to applications.
This vulnerability maps to CWE-129 in the Common Weakness Enumeration catalog, which covers improper validation of input boundaries. The flaw represents an input validation failure in the TCP option processing mechanism, where the system fails to properly validate the integrity and appropriateness of TCP options in established connections. From the MITRE ATT&CK framework perspective, this vulnerability could be leveraged as part of a broader attack chain under the network infiltration and persistence categories, potentially enabling more sophisticated attacks such as man-in-the-middle operations or service disruption.
The recommended mitigation strategies include applying the appropriate FreeBSD security patches that address the TCP option validation issue, upgrading to supported versions of the FreeBSD operating system where this vulnerability has been resolved, and implementing network-level controls such as intrusion detection systems to monitor for suspicious TCP packet patterns. Organizations should also consider implementing network segmentation and access controls to limit exposure of systems running vulnerable FreeBSD versions. Additionally, regular security auditing of network configurations and monitoring for anomalous TCP behavior can help detect exploitation attempts and provide early warning of potential compromises.