CVE-2005-0197 in IOS
Summary
by MITRE
Cisco IOS 12.1T, 12.2, 12.2T, 12.3 and 12.3T, with Multi Protocol Label Switching (MPLS) installed but disabled, allows remote attackers to cause a denial of service (device reload) via a crafted packet sent to the disabled interface.
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Analysis
by VulDB Data Team • 07/05/2025
Cisco IOS versions 12.1T through 12.3T contain a critical vulnerability in their Multi Protocol Label Switching implementation that can be exploited to trigger a device reload through crafted packet transmission. This vulnerability specifically affects systems where MPLS is installed but disabled, creating a dangerous condition where the device becomes susceptible to denial of service attacks. The flaw exists in how the system handles packet processing when MPLS is disabled, allowing remote attackers to craft specific packets that cause the router to crash and restart automatically. The vulnerability represents a classic buffer overflow or improper input validation issue that can be leveraged by attackers positioned outside the network perimeter to disrupt services without requiring authentication or privileged access. This weakness directly aligns with CWE-125, which describes out-of-bounds read vulnerabilities, and CWE-129, which covers insufficient validation of array index values. The impact of this vulnerability extends beyond simple service disruption as it can lead to complete network outages when critical routing devices are affected, particularly in enterprise or service provider environments where these routers serve as core infrastructure components.
The technical exploitation of this vulnerability occurs when an attacker sends specially crafted packets to an interface where MPLS has been installed but disabled. The system processes these packets through a code path that fails to properly validate packet contents or handle malformed data structures, leading to a memory corruption condition that ultimately results in a device reload. The attack vector is particularly concerning because it requires no authentication and can be executed from remote locations, making it a significant threat to network availability. The vulnerability demonstrates a clear failure in input sanitization and error handling within the IOS packet processing modules. Network administrators should note that the vulnerability is present regardless of whether MPLS is actively configured or simply installed on the device, meaning that even disabled functionality can serve as an attack surface. This characteristic aligns with the ATT&CK framework's T1499.004 technique for network denial of service, where adversaries leverage system weaknesses to disrupt availability. The flaw essentially creates a time-of-check to time-of-use vulnerability where the system's response to malformed packets triggers an immediate system restart without proper error recovery mechanisms.
The operational impact of this vulnerability can be severe for organizations relying on Cisco IOS routers for network infrastructure. When exploited successfully, the device reload causes immediate disruption to network services, potentially leading to cascading failures across interconnected systems. The vulnerability affects multiple IOS versions, increasing the potential attack surface significantly, and the fact that it can be triggered through disabled functionality means that organizations may not even be aware of the risk. This creates a dangerous situation where network administrators might assume that disabled features pose no threat to system stability. Organizations implementing network segmentation or using MPLS for specific services may be particularly vulnerable, as the attack can target any interface where the MPLS component is present. The vulnerability also demonstrates poor security practices in software design, where developers did not adequately consider the security implications of disabled features or the potential for malicious packet injection into system components. The lack of proper bounds checking in the packet handling code means that even legitimate network traffic could potentially trigger the vulnerability if crafted in the right way, making the attack surface broader than initially apparent.
Mitigation strategies for this vulnerability should focus on immediate patch application from Cisco, as the vendor has released specific software updates addressing this issue. Network administrators should prioritize patching affected routers, particularly those in critical network segments where availability is paramount. The implementation of network access control lists and packet filtering rules can provide temporary protection by blocking suspicious packet patterns, though this approach is less reliable than proper patching. Organizations should also consider disabling MPLS functionality entirely if it is not actively required, as this removes the attack surface entirely. Network monitoring systems should be enhanced to detect unusual reload patterns or packet injection attempts that may indicate exploitation attempts. Additionally, implementing redundant routing paths and failover mechanisms can help minimize the impact if a device does become compromised. The vulnerability serves as a reminder of the importance of comprehensive security testing for all installed features, not just active ones, and highlights the need for robust input validation across all network protocol implementations. Regular security assessments and vulnerability scanning should include verification of disabled features to ensure they do not present security risks. Organizations should also maintain detailed inventory records of all installed IOS features to quickly identify potential vulnerability exposure points.