CVE-2013-6694 in IOS
Summary
by MITRE
The IPSec implementation in Cisco IOS allows remote attackers to cause a denial of service (MTU change and tunnel-session drop) via crafted ICMP packets, aka Bug ID CSCul29918.
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Analysis
by VulDB Data Team • 12/23/2024
The vulnerability described in CVE-2013-6694 represents a critical flaw in Cisco IOS operating systems that affects the Internet Protocol Security (IPSec) implementation. This weakness specifically targets how the system processes incoming Internet Control Message Protocol packets, creating a pathway for remote attackers to disrupt network services. The issue manifests as a denial of service condition that impacts both Maximum Transmission Unit configuration and active tunnel sessions within the IPSec framework. The vulnerability was identified through Cisco's internal bug tracking system under the identifier CSCul29918, indicating its recognition as a significant security concern within the vendor's assessment process.
The technical root cause of this vulnerability lies in the improper handling of malformed ICMP packets within the IPSec processing pipeline of Cisco IOS devices. When the system receives crafted ICMP messages that contain specific payload structures or header values, the IPSec implementation fails to properly validate or sanitize these packets before processing them within the tunnel establishment and maintenance mechanisms. This processing error results in the system dynamically adjusting the Maximum Transmission Unit size and subsequently dropping active tunnel sessions. The flaw essentially creates a condition where legitimate network traffic can be disrupted through the injection of carefully constructed ICMP packets that exploit the lack of proper input validation in the IPSec subsystem.
From an operational perspective, this vulnerability poses significant risks to network availability and integrity, particularly in environments where IPSec tunnels are critical for secure communications. Attackers can leverage this weakness to create persistent disruptions in network connectivity, potentially affecting business continuity and secure remote access capabilities. The impact extends beyond simple service interruption as the MTU changes can cause fragmentation issues that cascade through the network stack, while tunnel session drops can force re-establishment of secure connections and potentially expose temporary network gaps in security coverage. Organizations relying on Cisco IOS for their network infrastructure face substantial operational risks when this vulnerability remains unpatched, as it can be exploited without requiring authentication credentials or specialized access privileges.
The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and represents a classic example of how insufficient input sanitization can lead to denial of service conditions in network security implementations. From an ATT&CK framework perspective, this vulnerability maps to techniques involving network denial of service and system compromise through manipulation of network protocols. The attack vector is particularly concerning as it operates at the network layer and requires no elevated privileges, making it accessible to any remote attacker who can send ICMP packets to the affected system. Organizations should implement immediate mitigation strategies including applying the relevant Cisco security patches, implementing network segmentation to limit exposure, and monitoring for anomalous ICMP traffic patterns that might indicate exploitation attempts. The vulnerability underscores the critical importance of proper input validation and robust error handling in security-critical network components, particularly within protocol implementations that handle untrusted network data.