CVE-2015-6267 in IOS XE
Summary
by MITRE
Cisco IOS XE before 2.2.3 on ASR 1000 devices allows remote attackers to cause a denial of service (Embedded Services Processor crash) via a crafted L2TP packet, aka Bug IDs CSCsw95722 and CSCsw95496.
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Analysis
by VulDB Data Team • 06/13/2022
The vulnerability described in CVE-2015-6267 represents a critical denial of service flaw affecting Cisco IOS XE software versions prior to 2.2.3 on ASR 1000 series devices. This issue specifically targets the Embedded Services Processor component within these networking appliances, which serves as a crucial subsystem responsible for handling various network services including Layer 2 Tunneling Protocol operations. The vulnerability arises from insufficient input validation mechanisms within the L2TP packet processing functionality, creating an exploitable condition that can be leveraged by remote attackers to disrupt network operations.
The technical flaw manifests when a maliciously crafted L2TP packet is transmitted to the affected device, triggering a memory corruption condition within the Embedded Services Processor. This memory corruption ultimately leads to a system crash and subsequent service disruption, effectively rendering the ASR 1000 device non-operational until manual intervention or system reboot occurs. The vulnerability is particularly concerning because it operates entirely at the network layer without requiring authentication or privileged access, making it highly accessible to potential attackers. The flaw stems from inadequate bounds checking and validation procedures within the L2TP processing code, which fails to properly sanitize incoming packet data before processing.
From an operational impact perspective, this vulnerability presents a significant risk to network infrastructure reliability and availability. Organizations relying on ASR 1000 devices for critical network services face potential disruption of their routing and switching operations, particularly in environments where these devices serve as primary or backup routing points. The remote nature of the attack means that adversaries can exploit this weakness from anywhere on the network, potentially causing cascading failures in network connectivity. The embedded processor crash creates a complete service outage that can last from several minutes to hours depending on the device recovery process and network redundancy configurations. This vulnerability directly impacts the availability aspect of the CIA triad and can be classified under CWE-129 as an insufficient input validation issue.
The attack vector for this vulnerability aligns with techniques documented in the MITRE ATT&CK framework under the T1499.004 sub-technique for Network Denial of Service, where adversaries specifically target network infrastructure components to create service disruptions. The exploitation requires minimal technical expertise as the attack can be executed through standard network packet crafting tools without requiring deep knowledge of the underlying system architecture. Network administrators face the challenge of detecting such attacks in transit, as the malicious packets appear as legitimate network traffic until they trigger the processing flaw. The vulnerability affects the device's ability to maintain stable network operations, potentially creating security gaps in network coverage while the device remains offline.
Mitigation strategies for this vulnerability should include immediate deployment of Cisco's recommended security patches and software updates to version 2.2.3 or later, which contain the necessary code fixes to properly validate L2TP packet inputs. Network segmentation and access control measures can help limit the attack surface by restricting unauthorized access to the affected devices. Implementing network monitoring solutions with anomaly detection capabilities can help identify unusual traffic patterns that may indicate exploitation attempts. Additionally, organizations should consider implementing rate limiting and packet filtering rules specifically targeting L2TP traffic to reduce the likelihood of successful exploitation. Regular vulnerability assessments and security audits should be conducted to identify similar weaknesses in network infrastructure components. The remediation process must include thorough testing of updated firmware in controlled environments before deployment to production networks to ensure compatibility and prevent unintended service disruptions.