CVE-2003-0567 in IOS
Summary
by MITRE
Cisco IOS 11.x and 12.0 through 12.2 allows remote attackers to cause a denial of service (traffic block) by sending a particular sequence of IPv4 packets to an interface on the device, causing the input queue on that interface to be marked as full.
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Analysis
by VulDB Data Team • 08/12/2025
Cisco IOS versions 11.x through 12.2 contain a critical vulnerability that enables remote attackers to execute denial of service attacks by transmitting specific IPv4 packet sequences to network interfaces. This flaw operates at the packet processing level within the input queue management system of the router operating system, fundamentally compromising network availability. The vulnerability manifests when the device receives malformed or specially crafted packets that trigger an abnormal state in the input queue handling mechanism, causing the queue to be permanently marked as full and subsequently blocking legitimate traffic flow.
The technical implementation of this vulnerability stems from insufficient validation of packet processing sequences within the IOS kernel. When the affected router receives packets that match specific patterns, the input queue management logic fails to properly handle the queue state transitions, resulting in the queue being marked as full even when it contains only a minimal number of packets. This condition persists until the device is manually rebooted or the queue is reset through administrative intervention. The flaw represents a classic case of improper resource management and queue state handling that falls under the CWE-362 weakness category, specifically addressing concurrent execution during resource management scenarios.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network infrastructure availability and reliability. Network administrators face the challenge of maintaining consistent connectivity when attackers can remotely trigger traffic blocking conditions that require manual intervention to resolve. The vulnerability affects all interfaces on the device that process IPv4 traffic, making it particularly dangerous in environments where routers serve as critical network gateways or transit points. Organizations using affected Cisco IOS versions may experience extended downtime periods while technicians diagnose and resolve the queue state issues, potentially leading to cascading failures in network infrastructure that depends on the compromised device.
Mitigation strategies for this vulnerability include immediate deployment of Cisco IOS patches and updates that address the input queue handling logic. Network administrators should implement access control lists to filter suspicious packet patterns and monitor interface queue states for abnormal conditions. The recommended approach involves upgrading to Cisco IOS versions that contain the specific fix for this vulnerability, which typically includes enhanced packet validation and improved queue management algorithms. Additionally, implementing network segmentation and rate limiting mechanisms can help reduce the impact of potential exploitation attempts while maintaining overall network functionality. This vulnerability aligns with ATT&CK technique T1498 which describes network denial of service attacks and demonstrates how improper input validation can lead to critical infrastructure availability issues. Organizations should also consider implementing intrusion detection systems that can identify and alert on suspicious packet sequences that match the vulnerability patterns, providing proactive monitoring capabilities to detect exploitation attempts before they cause service disruption.