CVE-2011-3276 in IOS
Summary
by MITRE
Unspecified vulnerability in the NAT implementation in Cisco IOS 12.1 through 12.4 and 15.0 through 15.1, and IOS XE 3.1.xSG, allows remote attackers to cause a denial of service (device reload or hang) by sending crafted SIP packets to TCP port 5060, aka Bug ID CSCso02147.
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Analysis
by VulDB Data Team • 11/23/2021
The vulnerability described in CVE-2011-3276 represents a critical flaw in Cisco IOS network operating systems that affects multiple versions including 12.1 through 12.4, 15.0 through 15.1, and IOS XE 3.1.xSG releases. This issue specifically targets the Network Address Translation implementation within Cisco IOS, creating a pathway for remote attackers to execute denial of service attacks against affected network devices. The vulnerability manifests when the system processes specially crafted Session Initiation Protocol packets transmitted to TCP port 5060, which is the standard port used for SIP communications in VoIP environments. The flaw operates at the network layer where the NAT functionality fails to properly handle malformed or unexpected SIP packet structures, leading to system instability and potential device crashes.
The technical nature of this vulnerability stems from inadequate input validation within the SIP processing module of the NAT implementation. When Cisco IOS receives SIP packets containing malformed headers, unexpected sequence numbers, or other irregularities in the packet structure, the system's parsing routines fail to properly handle these conditions. This parsing failure triggers an exception within the NAT subsystem that causes the device to either reload automatically or enter a hung state where it becomes unresponsive to network traffic. The vulnerability is particularly concerning because SIP is widely used in enterprise VoIP deployments, making affected devices prime targets for attackers seeking to disrupt communication services. According to CWE classification, this vulnerability maps to CWE-129 Input Validation, specifically involving improper handling of malformed input data within network protocol processing components.
The operational impact of this vulnerability extends beyond simple service disruption, as it can lead to complete network outages in environments where the affected devices serve as core routing or security appliances. Organizations relying on Cisco devices for voice communication services face significant business continuity risks when this vulnerability is exploited, as VoIP systems become unavailable and emergency communication channels may be compromised. The remote nature of the attack means that adversaries can exploit this flaw from outside the network perimeter, requiring minimal privileges and no authentication to execute successful attacks. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving denial of service and privilege escalation through protocol manipulation, specifically targeting network infrastructure components to achieve persistent service disruption.
Mitigation strategies for CVE-2011-3276 should prioritize immediate patch deployment through official Cisco security advisories, as the company released specific software updates addressing this NAT processing flaw. Network administrators should implement access control measures to restrict SIP traffic to trusted sources only, particularly by filtering TCP port 5060 traffic at network boundaries. Monitoring for unusual SIP packet patterns and implementing intrusion detection systems can help identify exploitation attempts before they succeed. Organizations should also consider deploying redundant network paths to minimize the impact of a successful attack, while conducting thorough vulnerability assessments to identify all potentially affected devices within their network infrastructure. The remediation process requires careful planning to avoid unintended service disruptions during patch deployment, particularly in mission-critical environments where network availability is paramount.