CVE-2014-2109 in IOS
Summary
by MITRE
The TCP Input module in Cisco IOS 12.2 through 12.4 and 15.0 through 15.4, when NAT is used, allows remote attackers to cause a denial of service (memory consumption or device reload) via crafted TCP packets, aka Bug IDs CSCuh33843 and CSCuj41494.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 05/09/2026
The vulnerability identified as CVE-2014-2109 represents a critical denial of service flaw within Cisco IOS operating systems that affects multiple software versions including 12.2 through 12.4 and 15.0 through 15.4. This issue specifically impacts the TCP Input module when Network Address Translation is actively configured, creating a pathway for remote attackers to exploit the system through carefully crafted TCP packets. The vulnerability manifests as a memory consumption issue or device reload condition that can completely disrupt network services and availability. The bug was catalogued under two distinct identifiers CSCuh33843 and CSCuj41494, indicating the complexity and severity of the underlying issue within the TCP processing stack of affected Cisco IOS versions.
The technical flaw stems from improper handling of TCP packets within the TCP Input module when NAT is enabled, creating a condition where malformed or specially constructed TCP segments can trigger excessive memory allocation or processing overhead. When these crafted packets are processed by the affected Cisco IOS devices, they cause the system to consume increasing amounts of memory or force an automatic device reload to prevent system instability. This behavior occurs because the TCP processing logic fails to properly validate or limit the resources consumed during packet handling when NAT is active, leading to a resource exhaustion condition that ultimately results in service disruption. The vulnerability is particularly dangerous as it can be exploited remotely without requiring authentication, making it accessible to any attacker who can send TCP packets to the affected device.
The operational impact of CVE-2014-2109 is severe and far-reaching across enterprise and service provider networks that rely on Cisco IOS devices for routing and network services. Organizations using affected IOS versions with NAT configurations face potential network outages, service interruptions, and complete device unavailability that can affect critical business operations and customer connectivity. The vulnerability can be exploited to cause sustained denial of service conditions that may require manual intervention to restore normal operations, including device reboots and configuration changes. Network administrators may experience cascading effects throughout their infrastructure as the denial of service impacts routing protocols, connectivity to external services, and overall network stability. The remote exploitability means that attackers can target these vulnerabilities from outside the network perimeter, making them particularly dangerous for organizations with exposed network services.
Mitigation strategies for CVE-2014-2109 should prioritize immediate software updates and patches from Cisco to address the underlying TCP processing flaw. Organizations must implement the latest IOS software releases that contain fixes for this vulnerability, particularly focusing on versions that have been specifically tested and validated for compatibility with existing network configurations. Network segmentation and access control measures should be enhanced to limit exposure of affected devices to untrusted network segments. Implementing TCP SYN cookies and rate limiting mechanisms can help reduce the impact of crafted packet attacks while defensive network monitoring should be enabled to detect unusual memory consumption patterns or device reload events. Additionally, administrators should consider disabling NAT functionality on affected devices if it is not essential for network operations, as this removes the specific condition that triggers the vulnerability. The mitigation approach should align with industry best practices and security frameworks such as those recommended by the Center for Internet Security and NIST guidelines for network security management.