CVE-2012-3955 in DHCP
Summary
by MITRE
ISC DHCP 4.1.x before 4.1-ESV-R7 and 4.2.x before 4.2.4-P2 allows remote attackers to cause a denial of service (daemon crash) in opportunistic circumstances by establishing an IPv6 lease in an environment where the lease expiration time is later reduced.
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Analysis
by VulDB Data Team • 04/13/2021
The vulnerability identified as CVE-2012-3955 affects ISC DHCP versions prior to 4.1-ESV-R7 and 4.2.4-P2, representing a significant denial of service flaw that can be exploited remotely under specific conditions. This vulnerability resides within the DHCP daemon implementation and demonstrates how seemingly minor configuration changes can lead to critical system instability. The issue specifically manifests when an IPv6 lease is established in an environment where the lease expiration time is subsequently reduced, creating a race condition that leads to daemon crash. The vulnerability operates under the context of network infrastructure services where DHCP servers maintain state information about client leases, making it particularly dangerous in production environments where continuous availability is critical. According to CWE classification, this vulnerability maps to CWE-129, which addresses improper validation of length of input data, as the daemon fails to properly validate lease duration parameters during active lease management operations.
The technical flaw involves a buffer manipulation issue within the DHCP daemon's IPv6 lease handling mechanism. When a client establishes an IPv6 lease and the server subsequently reduces the lease expiration time, the daemon's internal state management becomes inconsistent, leading to memory corruption and eventual crash. The vulnerability exploits the timing relationship between lease creation and lease duration modification, where opportunistic circumstances create the perfect conditions for exploitation. This occurs because the DHCP server does not properly validate that lease expiration times remain consistent with existing lease states, allowing malformed or contradictory lease parameters to cause memory management errors. The daemon's handling of IPv6-specific lease structures introduces additional complexity, as the IPv6 addressing scheme requires more sophisticated state tracking than IPv4. This vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks targeting infrastructure services.
The operational impact of CVE-2012-3955 extends beyond simple service disruption, as DHCP daemon crashes can lead to complete network partitioning in environments where the DHCP server serves as a critical infrastructure component. When the daemon crashes, all active DHCP services cease functioning, requiring manual intervention to restart the service and potentially causing network outages for connected devices. The opportunistic nature of the vulnerability means that exploitation may not always be immediately apparent, as it depends on specific environmental conditions and timing sequences. Organizations using affected ISC DHCP versions face significant risk in mission-critical environments where continuous network availability is essential. The vulnerability's remote exploitability means that attackers can trigger the denial of service without requiring physical access or local network presence, making it particularly dangerous in public or shared network environments. Network administrators must consider the cascading effects of such a vulnerability, as DHCP service disruption can impact authentication systems, network access controls, and other services that depend on dynamic IP address assignment.
Mitigation strategies for CVE-2012-3955 require immediate patch application to affected ISC DHCP versions, with administrators prioritizing updates to 4.1-ESV-R7 or 4.2.4-P2 releases. Organizations should implement network monitoring to detect potential exploitation attempts and establish automated alerting for DHCP daemon crashes or restarts. Configuration reviews should focus on lease duration management policies to prevent scenarios where lease expiration times are reduced during active lease periods. Network segmentation and redundancy measures can help minimize the impact of potential exploitation by isolating critical services and maintaining backup DHCP infrastructure. Security teams should also consider implementing intrusion detection systems that can monitor for anomalous DHCP traffic patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper input validation and state management in network infrastructure services, as it demonstrates how inconsistent parameter handling can lead to complete service failure. Organizations should conduct comprehensive vulnerability assessments to identify other potential race conditions in their DHCP implementations and related network services. The remediation process should include thorough testing of updated DHCP configurations to ensure that the patch does not introduce compatibility issues with existing network infrastructure components.