CVE-2002-1768 in IOS
Summary
by MITRE
Cisco IOS 11.1 through 12.2, when HSRP support is not enabled, allows remote attackers to cause a denial of service (CPU consumption) via randomly sized UDP packets to the Hot Standby Routing Protocol (HSRP) port 1985.
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Analysis
by VulDB Data Team • 05/26/2019
Cisco IOS versions 11.1 through 12.2 contain a significant denial of service vulnerability in their handling of Hot Standby Routing Protocol traffic when HSRP functionality is not actively enabled on the device. This vulnerability manifests when the system receives UDP packets of varying sizes on the designated HSRP port 1985, leading to excessive cpu consumption and potential system instability. The flaw exists in the protocol parsing logic where the router processes these packets even when HSRP is disabled, causing the system to allocate resources unnecessarily for protocol handling that should not be active. This vulnerability directly maps to CWE-400, which describes unspecified resource exhaustion issues, and specifically relates to improper handling of network protocol traffic in the context of routing protocols. The attack vector requires only remote access to send malformed or randomly sized UDP packets to the target router, making it particularly dangerous as it can be exploited from outside the network perimeter without requiring authentication or privileged access.
The operational impact of this vulnerability extends beyond simple service disruption as the excessive cpu consumption can lead to complete system instability and potential routing failures within the network. When a router becomes overwhelmed with processing these packets, legitimate traffic may be dropped or delayed, creating cascading effects throughout the network infrastructure that relies on proper routing functionality. The vulnerability affects the core routing protocols implementation within Cisco IOS, specifically targeting the HSRP protocol handling mechanism that should only be active when HSRP is explicitly configured and enabled. This represents a fundamental flaw in protocol state management where the system fails to properly distinguish between active and inactive protocol handling, leading to unnecessary resource allocation. The vulnerability also aligns with ATT&CK technique T1498 which describes denial of service attacks targeting network infrastructure and can be classified under the broader category of network protocol manipulation attacks.
Mitigation strategies for this vulnerability should focus on implementing proper network segmentation and access control measures to restrict access to the HSRP port 1985 from unauthorized sources. Network administrators should configure access control lists to filter traffic on port 1985 and ensure that HSRP is only enabled on devices where it is actually required. The most effective immediate solution involves upgrading to Cisco IOS versions that have patched this vulnerability, as Cisco released specific fixes for affected versions in their security bulletins. Additionally, implementing rate limiting mechanisms and monitoring for unusual traffic patterns on the HSRP port can help detect and prevent exploitation attempts. Organizations should also consider implementing network intrusion detection systems that can identify and alert on suspicious UDP traffic patterns targeting the HSRP port, providing early warning capabilities for potential attacks. The vulnerability highlights the importance of proper protocol state management and the need for robust input validation in network infrastructure devices, particularly in routing protocols that handle critical network functionality.