CVE-2015-2923 in FreeBSD
Summary
by MITRE
The Neighbor Discovery (ND) protocol implementation in the IPv6 stack in FreeBSD through 10.1 allows remote attackers to reconfigure a hop-limit setting via a small hop_limit value in a Router Advertisement (RA) message.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 05/02/2022
The vulnerability identified as CVE-2015-2923 represents a critical flaw in the IPv6 Neighbor Discovery protocol implementation within FreeBSD operating systems versions 10.1 and earlier. This issue specifically targets the Router Advertisement message handling mechanism, which is fundamental to IPv6 network configuration and operation. The vulnerability arises from insufficient validation of hop_limit values in Router Advertisement messages, creating a potential attack vector that could allow remote adversaries to manipulate core network parameters.
The technical flaw exists in how the FreeBSD IPv6 stack processes Router Advertisement messages containing malformed hop_limit values. When a malicious actor sends a Router Advertisement packet with an intentionally small hop_limit value, the system fails to properly validate this parameter before applying it to the network configuration. This validation failure enables attackers to override the default hop-limit setting that typically controls how many hops a packet can traverse before being discarded. The hop_limit parameter is crucial for preventing packet loops and managing network traffic flow, making this vulnerability particularly dangerous for network stability and security.
The operational impact of this vulnerability extends beyond simple network disruption to potentially enable more sophisticated attacks within the compromised network environment. An attacker who successfully exploits this vulnerability can manipulate the hop-limit setting to either reduce network visibility by limiting packet traversal or increase network load by forcing packets to traverse unnecessary paths. This capability aligns with attack techniques described in the MITRE ATT&CK framework under network denial of service and network configuration modification tactics. The vulnerability could enable attackers to disrupt network services, create routing anomalies, or potentially facilitate further attacks by manipulating network topology information.
From a cybersecurity perspective, this vulnerability demonstrates the critical importance of proper input validation in network protocol implementations. The flaw directly relates to CWE-20, which addresses "Improper Input Validation" in software security design. The issue highlights the need for robust parameter validation in protocol implementations, particularly in core networking components that handle external communications. Organizations running FreeBSD systems were exposed to potential network compromise, as the vulnerability could be exploited without requiring authentication or privileged access. The security implications extend to network infrastructure management, where such manipulation could go undetected while causing significant operational disruption.
The recommended mitigation strategy involves applying the official FreeBSD security patches that address the hop_limit validation issue in Router Advertisement processing. System administrators should prioritize updating to FreeBSD versions 10.2 or later, where the vulnerability has been resolved through proper parameter validation in the IPv6 stack implementation. Network monitoring should be enhanced to detect unusual Router Advertisement patterns or hop_limit value changes that could indicate exploitation attempts. Additionally, implementing network segmentation and access controls can help limit the potential impact of successful exploitation attempts, while maintaining proper network logging and alerting mechanisms to detect anomalous network behavior that might indicate an active attack.