CVE-2015-4191 in IOS XR
Summary
by MITRE
Cisco IOS XR 5.2.1 allows remote attackers to cause a denial of service (ipv6_io service reload) via a malformed IPv6 packet, aka Bug ID CSCuq95565.
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Analysis
by VulDB Data Team • 07/01/2017
Cisco IOS XR 5.2.1 contains a critical vulnerability that enables remote attackers to trigger a denial of service condition through manipulation of IPv6 packet structures. This vulnerability specifically targets the ipv6_io service within the routing platform, causing the system to reload automatically when processing malformed IPv6 packets. The flaw represents a classic buffer overflow condition where the device fails to properly validate incoming IPv6 packet headers, leading to unexpected service interruption. The vulnerability has been catalogued under Cisco Bug ID CSCuq95565 and demonstrates a significant weakness in the platform's packet processing mechanisms that could be exploited without authentication.
The technical exploitation of this vulnerability occurs when an attacker crafts a malformed IPv6 packet that contains unexpected data within the packet headers or payload sections. The ipv6_io service within IOS XR fails to properly sanitize these malformed packets, causing the service to crash and subsequently reload the entire routing process. This behavior creates a cascading effect that can disrupt network connectivity and routing operations across the affected device. The vulnerability specifically affects the IPv6 processing stack, where the system does not implement adequate input validation procedures to handle malformed packet structures. This type of flaw aligns with CWE-129, which describes issues related to insufficient validation of length fields, and represents a failure in proper bounds checking within the network processing code.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise network stability and availability. When the ipv6_io service reloads, it can cause temporary loss of routing functionality and may require manual intervention to restore normal operations. Network administrators face the challenge of maintaining service availability while the system recovers from the automatic reload, which can be particularly problematic in mission-critical environments where continuous network operation is essential. The vulnerability affects devices running IOS XR 5.2.1 and potentially other versions in the same release cycle, making it a widespread concern across enterprise and service provider networks that utilize Cisco's routing platforms. The attack vector requires only network access to send the malformed packets, making it particularly dangerous as it can be exploited from external networks without requiring additional privileges.
Mitigation strategies for this vulnerability should focus on implementing network segmentation and access control measures to limit exposure to untrusted networks. Network administrators should consider deploying intrusion detection systems that can identify and block malformed IPv6 packets before they reach the vulnerable service. The most effective immediate solution involves applying Cisco's official security patches and software updates that address the specific buffer overflow condition in the ipv6_io service. Organizations should also implement monitoring procedures to detect unusual service reload patterns that may indicate exploitation attempts. From a defensive perspective, this vulnerability aligns with ATT&CK technique T1499.002, which covers network denial of service attacks, and represents a common attack pattern where adversaries leverage protocol implementation flaws to disrupt network services. Regular security assessments and vulnerability scanning should be conducted to identify similar weaknesses in other network components and ensure comprehensive protection against similar exploitation vectors.