CVE-2015-0769 in IOS XR
Summary
by MITRE
Cisco IOS XR 4.0.1 through 4.2.0 for CRS-3 Carrier Routing System allows remote attackers to cause a denial of service (NPU ASIC scan and line-card reload) via crafted IPv6 extension headers, aka Bug ID CSCtx03546.
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Analysis
by VulDB Data Team • 05/21/2022
The vulnerability identified as CVE-2015-0769 affects Cisco IOS XR software versions 4.0.1 through 4.2.0 running on CRS-3 Carrier Routing System devices. This represents a critical denial of service flaw that can be exploited remotely by attackers to disrupt network operations. The vulnerability specifically targets the Network Processing Unit ASIC scanning mechanisms and line-card reload functionality within the routing system, fundamentally compromising the availability of network services. The issue stems from improper handling of crafted IPv6 extension headers, which when processed by the affected Cisco IOS XR implementations trigger unexpected system behavior leading to complete service disruption.
The technical root cause of this vulnerability lies in the insufficient validation and processing of IPv6 extension headers within the IOS XR software stack. When maliciously crafted IPv6 packets containing specially constructed extension headers are transmitted to affected CRS-3 devices, the system's packet processing engines fail to properly handle these malformed headers. This processing failure causes the Network Processing Unit ASIC to enter an abnormal state where it continuously scans for packets and subsequently triggers line-card reload operations. The vulnerability maps to CWE-129, which describes improper validation of input boundaries, and specifically relates to inadequate input validation in network protocol handling components. The flaw demonstrates characteristics of CWE-347, indicating improper validation of cryptographic signatures, though in this case it's related to packet header validation rather than cryptographic elements.
The operational impact of this vulnerability extends beyond simple service disruption to encompass complete network reliability degradation. Network operators utilizing affected CRS-3 systems face the risk of sustained denial of service conditions that can persist until manual intervention occurs through device reload or configuration changes. The automatic line-card reload mechanism, designed as a recovery feature, becomes a vector for prolonged service interruption when triggered by malicious inputs. This vulnerability affects network infrastructure critical for service provider operations, potentially causing cascading failures across connected networks. The attack vector requires only remote network access to transmit specially crafted IPv6 packets, making it particularly dangerous as it can be exploited from external network locations without requiring physical access to the affected devices.
Mitigation strategies for CVE-2015-0769 should prioritize immediate implementation of software updates from Cisco to address the vulnerability. Network administrators must apply the relevant security patches and firmware updates provided by Cisco to resolve the flawed packet processing logic. Additionally, network segmentation and access control measures should be implemented to limit exposure to the affected systems, particularly at network boundaries where IPv6 traffic is permitted. The implementation of ingress filtering and IPv6 header validation rules can help prevent malicious packets from reaching vulnerable systems. Organizations should also consider implementing monitoring solutions to detect unusual patterns in NPU scanning activities or line-card reload operations that might indicate exploitation attempts. From an ATT&CK framework perspective, this vulnerability aligns with T1499.002, which covers network denial of service attacks, and T1071.004, covering application layer protocols, particularly focusing on IPv6 protocol handling weaknesses. The vulnerability demonstrates the importance of robust input validation in network infrastructure software and underscores the need for comprehensive security testing of protocol implementations in carrier-grade networking equipment.