CVE-2012-3571 in DHCP
Summary
by MITRE
ISC DHCP 4.1.2 through 4.2.4 and 4.1-ESV before 4.1-ESV-R6 allows remote attackers to cause a denial of service (infinite loop and CPU consumption) via a malformed client identifier.
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Analysis
by VulDB Data Team • 09/17/2024
The vulnerability identified as CVE-2012-3571 affects ISC DHCP server versions 4.1.2 through 4.2.4 and 4.1-ESV versions before 4.1-ESV-R6, representing a critical denial of service weakness that can be exploited remotely by attackers to consume excessive CPU resources. This vulnerability specifically targets the client identifier parsing mechanism within the DHCP implementation, where malformed client identifiers can trigger an infinite loop in the server's processing logic. The flaw exists in the way the DHCP server handles client identifiers during the lease negotiation process, creating a condition where the server enters an endless processing cycle that consumes 100% of available CPU resources, effectively rendering the service unavailable to legitimate clients.
The technical root cause of this vulnerability lies in inadequate input validation and error handling within the DHCP server's client identifier processing code. When a malformed client identifier is received in a DHCP request, the server's parsing routine fails to properly validate the identifier format and does not implement appropriate bounds checking or loop termination conditions. This allows an attacker to craft specially formatted client identifiers that cause the server to enter an infinite loop during processing, with the loop typically occurring in the client identifier validation or parsing functions. The vulnerability maps to CWE-835, which describes the weakness of an infinite loop or other loop that never terminates, and can be classified under the ATT&CK technique T1499.1 for network denial of service attacks. The issue is particularly severe because it requires no authentication or privileged access to exploit, making it a high-impact vulnerability that can be leveraged by any remote attacker with network access to the affected DHCP server.
The operational impact of this vulnerability extends beyond simple service disruption, as it can lead to complete network outages when multiple attackers target the same DHCP server or when the server is part of a critical infrastructure component. The infinite loop consumes CPU resources at maximum capacity, preventing the server from processing legitimate DHCP requests from authorized clients, which can result in network connectivity issues for all devices relying on that DHCP service. Organizations with multiple DHCP servers or those using DHCP failover configurations may experience cascading failures if the vulnerability is exploited across different server instances. The vulnerability affects both IPv4 and IPv6 DHCP implementations within the affected versions, making it particularly dangerous in environments that utilize dual-stack networking or transitional protocols. Attackers can easily exploit this vulnerability using simple network scanning tools or automated scripts that generate malformed client identifiers, making it a popular target for low-skill attackers seeking to disrupt network services.
Mitigation strategies for CVE-2012-3571 primarily focus on upgrading to patched versions of ISC DHCP server software, specifically versions 4.2.5, 4.1-ESV-R6, and later releases that contain the necessary code fixes. Organizations should prioritize immediate patch deployment across all affected DHCP server instances, particularly those serving critical network infrastructure or high-traffic environments. Additional defensive measures include implementing network segmentation to isolate DHCP servers from untrusted networks, deploying intrusion detection systems to monitor for malformed DHCP requests, and configuring rate limiting or request filtering mechanisms to detect and block suspicious client identifier patterns. Network administrators should also consider implementing DHCP snooping features and DHCP relay configurations to add additional layers of protection. The vulnerability demonstrates the importance of proper input validation and defensive programming practices in network services, as similar issues can be prevented through comprehensive testing of edge case inputs and implementation of appropriate timeout mechanisms. Organizations should conduct regular vulnerability assessments of their DHCP infrastructure and maintain up-to-date patch management procedures to prevent exploitation of similar vulnerabilities in the future.