CVE-2011-2549 in IOS XR
Summary
by MITRE
Unspecified vulnerability in Cisco IOS XR 4.1.x before 4.1.1 on Cisco Aggregation Services Routers (ASR) 9000 series devices allows remote attackers to cause a denial of service (line-card reload) via an IPv4 packet, aka Bug ID CSCtr26695.
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Analysis
by VulDB Data Team • 03/28/2017
The vulnerability identified as CVE-2011-2549 represents a critical denial of service flaw within Cisco IOS XR software version 4.1.x prior to 4.1.1, specifically affecting the ASR 9000 series aggregation services routers. This issue manifests through an unspecified weakness in the processing of IPv4 packets, creating a pathway for remote attackers to deliberately trigger system instability. The vulnerability impacts the line-card functionality of these high-end networking devices, which serve as core infrastructure components in telecommunications networks and enterprise environments. The ASR 9000 series routers are designed for high-capacity data aggregation and routing, making their reliability essential for network operations. When exploited, this vulnerability enables attackers to force line-card reloads, effectively disrupting network services and potentially causing cascading failures across interconnected systems.
The technical nature of this vulnerability resides in the improper handling of IPv4 packet processing within the IOS XR operating system's network stack implementation. Attackers can craft and transmit specifically formatted IPv4 packets that, when processed by the vulnerable router, trigger an internal error condition leading to the automatic reload of the affected line-card module. This behavior demonstrates a lack of proper input validation and error handling mechanisms within the packet processing pipeline. The vulnerability's remote exploitability means that attackers do not require physical access or local network presence to execute the attack, making it particularly dangerous in publicly accessible network environments. The line-card reload operation effectively removes the affected hardware module from service, causing temporary network disruption and requiring manual intervention or automatic failover processes to restore normal operations.
The operational impact of CVE-2011-2549 extends beyond simple service disruption, as line-card reloads can compromise network stability and availability in mission-critical environments. For telecommunications providers and enterprise networks relying on ASR 9000 series equipment, this vulnerability presents a significant risk to service level agreements and network uptime requirements. The attack can be executed from any location with network connectivity to the vulnerable device, making it difficult to defend against through traditional network segmentation approaches. Network administrators face challenges in detecting and mitigating such attacks, as the malicious packets may appear legitimate to network monitoring systems. The vulnerability also has implications for network resilience, as the automatic reload process can cause temporary loss of routing services and may trigger cascading failures in redundant network architectures. Organizations using affected Cisco IOS XR versions must consider the potential for extended service outages and the associated costs of manual intervention and system recovery.
Mitigation strategies for this vulnerability center on applying the official Cisco security patches and software updates released to address the specific flaw. Organizations should prioritize upgrading their ASR 9000 series routers to IOS XR 4.1.1 or later versions that contain the necessary fixes. Network segmentation and access control measures can provide temporary protection by limiting network exposure and reducing the attack surface available to potential adversaries. Implementing packet filtering rules at network perimeters to block suspicious IPv4 traffic patterns may help reduce the risk of exploitation, though this approach is not foolproof given the remote nature of the attack vector. Monitoring network logs for unusual line-card reload events and implementing intrusion detection systems can help detect potential exploitation attempts. The vulnerability aligns with CWE-119, which addresses improper restriction of operations within a limited access scope, and represents a classic example of how insufficient input validation can lead to system instability. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique for network denial of service attacks, demonstrating how network infrastructure devices can be targeted to disrupt service availability. Organizations should also consider implementing automated patch management processes to ensure timely deployment of security updates and maintain comprehensive network inventory tracking to identify all vulnerable devices across their infrastructure.