CVE-2004-1111 in IOS
Summary
by MITRE
Cisco IOS 2.2(18)EW, 12.2(18)EWA, 12.2(14)SZ, 12.2(18)S, 12.2(18)SE, 12.2(18)SV, 12.2(18)SW, and other versions without the "no service dhcp" command, keep undeliverable DHCP packets in the queue instead of dropping them, which allows remote attackers to cause a denial of service (dropped traffic) via multiple undeliverable DHCP packets that exceed the input queue size.
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Analysis
by VulDB Data Team • 07/06/2025
This vulnerability exists in multiple versions of Cisco IOS software where the system fails to properly handle undeliverable DHCP packets, creating a potential denial of service condition. The flaw specifically affects Cisco IOS versions 2.2(18)EW, 12.2(18)EWA, 12.2(14)SZ, 12.2(18)S, 12.2(18)SE, 12.2(18)SV, 12.2(18)SW, and other affected releases. When these systems receive DHCP packets that cannot be delivered due to network issues or misconfigurations, they queue these packets instead of dropping them immediately, leading to resource exhaustion.
The technical mechanism behind this vulnerability involves the input queue management system within Cisco IOS. Normally, when a packet cannot be delivered to its intended destination, the system should drop the packet to prevent queue buildup. However, in affected versions, the system retains these undeliverable DHCP packets in the input queue indefinitely. This behavior creates a memory exhaustion scenario where the queue fills up with stale packets, eventually consuming all available memory resources. The vulnerability is particularly dangerous because DHCP packets are commonly sent and can be easily generated by remote attackers.
The operational impact of this vulnerability is significant as it allows remote attackers to perform a denial of service attack against affected Cisco devices. Attackers can simply send multiple undeliverable DHCP packets to the target system, causing the input queue to overflow and resulting in dropped traffic. This creates a situation where legitimate network traffic is disrupted, effectively denying service to authorized users. The attack requires minimal resources from the attacker side, making it particularly dangerous as it can be executed from remote locations without requiring special privileges or extensive knowledge of the target system.
This vulnerability maps to CWE-129 in the Common Weakness Enumeration, specifically addressing improper handling of input validation and resource management issues. The attack pattern aligns with the MITRE ATT&CK framework under the T1498 technique for Network Denial of Service, where adversaries exploit weaknesses in network protocols to disrupt service availability. The vulnerability also reflects poor input queue management practices and inadequate resource limiting mechanisms within the IOS operating system.
The recommended mitigation strategy involves implementing the "no service dhcp" command on affected Cisco IOS devices, which disables the DHCP service entirely and prevents the problematic queueing behavior. Network administrators should also consider implementing rate limiting mechanisms and monitoring for unusual DHCP traffic patterns. Additionally, applying the latest security patches from Cisco that address this specific vulnerability is essential for long-term protection. Regular network monitoring and traffic analysis should be implemented to detect potential exploitation attempts and ensure that input queues do not become overloaded with stale packets.