CVE-2012-4620 in IOS
Summary
by MITRE
Cisco IOS 12.2 and 15.0 through 15.2 on Cisco 10000 series routers, when a tunnel interface exists, allows remote attackers to cause a denial of service (interface queue wedge) via tunneled (1) GRE/IP, (2) IPIP, or (3) IPv6 in IPv4 packets, aka Bug ID CSCts66808.
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Analysis
by VulDB Data Team • 04/14/2021
The vulnerability described in CVE-2012-4620 represents a critical denial of service flaw affecting Cisco IOS versions 12.2 and 15.0 through 15.2 running on Cisco 10000 series routers. This issue specifically manifests when tunnel interfaces are present on the affected devices, creating a scenario where remote attackers can exploit malformed packet structures to trigger interface queue wedges that effectively render network services unavailable. The vulnerability impacts the fundamental packet processing capabilities of these routers, making it particularly dangerous in enterprise and service provider environments where continuous network availability is paramount.
The technical flaw resides in how Cisco IOS handles specific types of tunneled packets when they traverse tunnel interfaces configured on the affected routers. The vulnerability specifically affects three tunneling protocols: Generic Routing Encapsulation over IP, IP in IP tunneling, and IPv6 in IPv4 encapsulation. When these particular packet types are received and processed by the router's tunnel interface handling code, a condition occurs that causes the interface queue to become wedged, preventing further packet processing on that specific interface. This queue wedging behavior represents a classic denial of service vector where legitimate network traffic is blocked due to the router's inability to properly handle the malformed tunneled packets. The flaw operates at the network protocol processing layer, specifically within the router's packet forwarding and tunneling mechanisms, and can be triggered remotely without requiring authentication or privileged access.
The operational impact of this vulnerability extends beyond simple service disruption, as it can cause cascading effects throughout the network infrastructure. When an interface queue wedges, the affected tunnel interface becomes non-functional, potentially disrupting all traffic flowing through that interface including critical business applications, voice services, and data communications. In large enterprise networks or service provider environments where multiple tunnel interfaces exist, attackers could strategically target specific interfaces to maximize disruption. The vulnerability's remote exploitability means that attackers located anywhere on the network can trigger the condition, making it particularly dangerous for perimeter devices that handle external traffic. This issue directly relates to CWE-129 and CWE-476 within the Common Weakness Enumeration framework, representing weaknesses in input validation and resource management that can lead to denial of service conditions.
Mitigation strategies for CVE-2012-4620 should focus on both immediate defensive measures and long-term architectural improvements. Network administrators should implement access control lists to filter out malformed tunnel packets, particularly those matching the vulnerable protocols, while also applying the latest security patches from Cisco that address the specific queue wedging condition. The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for network denial of service, highlighting the importance of monitoring for unusual traffic patterns and interface queue behavior. Organizations should also consider implementing redundant network paths and failover mechanisms to ensure that the failure of a single interface does not completely disrupt network services. Additionally, regular network traffic monitoring and anomaly detection systems should be configured to identify potential exploitation attempts, as the queue wedging condition may manifest as unusual interface utilization patterns or packet processing delays that precede complete service disruption.