CVE-2006-0340 in IOS
Summary
by MITRE
Unspecified vulnerability in Stack Group Bidding Protocol (SGBP) support in Cisco IOS 12.0 through 12.4 running on various Cisco products, when SGBP is enabled, allows remote attackers on the local network to cause a denial of service (device hang and network traffic loss) via a crafted UDP packet to port 9900.
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Analysis
by VulDB Data Team • 06/23/2025
The vulnerability described in CVE-2006-0340 represents a critical flaw in Cisco IOS software that affects versions 12.0 through 12.4 across multiple Cisco network devices. This issue specifically impacts the Stack Group Bidding Protocol implementation, which is a mechanism used by Cisco switches to establish and maintain stack connections between multiple devices. The SGBP protocol operates on UDP port 9900 and is designed to facilitate communication between stacked switches to determine which device will serve as the master in the stack configuration. When this protocol is enabled on affected Cisco IOS versions, it creates a pathway for remote attackers to exploit a flaw that can result in complete service disruption.
The technical nature of this vulnerability stems from inadequate input validation within the SGBP implementation within Cisco IOS. When a specially crafted UDP packet is sent to port 9900, the device fails to properly handle the malformed data, leading to a system crash or hang condition that renders the device non-responsive. This flaw operates at the network protocol level and does not require authentication or specific privileges to exploit, making it particularly dangerous as it can be triggered from any device on the local network segment. The vulnerability's impact extends beyond simple device restarts, as it can cause complete network traffic loss and disrupt the entire stack configuration, potentially leading to widespread network outages that affect multiple services and applications relying on the switched network infrastructure.
The operational impact of this vulnerability is severe and multifaceted, as it can be exploited by malicious actors within the local network to perform denial of service attacks against critical network infrastructure. Network administrators face the challenge of having to either disable the SGBP protocol entirely, which removes a valuable stack management feature, or apply time-sensitive patches that may require device restarts and could potentially introduce compatibility issues with existing network configurations. The vulnerability's exploitation can result in extended periods of network downtime, service disruption for end users, and significant operational costs associated with troubleshooting and recovery efforts. Organizations with stacked switch configurations are particularly vulnerable, as the attack can compromise the entire stack hierarchy and potentially cascade to affect larger network segments.
Mitigation strategies for CVE-2006-0340 should focus on immediate network segmentation and access control measures to prevent unauthorized access to the local network segment where affected devices reside. Network administrators should implement firewall rules to block UDP traffic to port 9900 from untrusted networks and consider disabling SGBP functionality on devices where it is not strictly required for stack management operations. The most effective long-term solution involves applying Cisco's official security patches and updates that address the specific input validation flaws in the SGBP implementation. According to CWE standards, this vulnerability aligns with CWE-129 which covers improper validation of input boundaries, and the attack pattern corresponds to the ATT&CK technique T1499.004 for network denial of service. Organizations should also conduct thorough network assessments to identify all affected devices and implement monitoring solutions to detect potential exploitation attempts, as the vulnerability's impact can be difficult to distinguish from other network issues without proper forensic analysis and logging capabilities.