CVE-2015-0618 in IOS XR
Summary
by MITRE
Cisco IOS XR 5.0.1 and 5.2.1 on Network Convergence System (NCS) 6000 devices and 5.1.3 and 5.1.4 on Carrier Routing System X (CRS-X) devices allows remote attackers to cause a denial of service (line-card reload) via malformed IPv6 packets with extension headers, aka Bug ID CSCuq95241.
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Analysis
by VulDB Data Team • 03/10/2022
The vulnerability described in CVE-2015-0618 represents a critical denial of service flaw affecting Cisco IOS XR software versions 5.0.1 and 5.2.1 on Network Convergence System NCS 6000 devices, as well as versions 5.1.3 and 5.1.4 on Carrier Routing System X devices. This vulnerability specifically targets the handling of IPv6 packets containing malformed extension headers, creating a condition that can trigger automatic line-card reloads. The issue manifests as a remote attack vector, allowing adversaries to exploit the flaw from outside the network perimeter without requiring authentication credentials or physical access to the affected hardware.
The technical root cause of this vulnerability lies in the improper validation of IPv6 extension headers within the IOS XR routing software implementation. When the system receives IPv6 packets with malformed or malformed extension headers, the processing routine fails to properly handle the unexpected data structure, leading to an uncontrolled system state that ultimately results in the automatic reload of the affected line card. This behavior demonstrates a classic buffer overflow or input validation vulnerability where the software does not adequately sanitize incoming network traffic before processing it. The vulnerability maps to CWE-129, which describes improper validation of input boundaries, and CWE-248, which addresses an exception not caught by the application.
The operational impact of this vulnerability extends beyond simple service disruption, as it can cause significant network instability and potential service degradation across the entire routing infrastructure. When a line card reload occurs, it temporarily removes the affected hardware from service, potentially disrupting traffic flows that were being handled by that specific card. In large-scale deployments with multiple line cards, this could result in cascading failures or temporary network partitions. The vulnerability's remote exploitability means that attackers can trigger these reloads from anywhere on the internet, making it particularly dangerous in production environments where network availability is critical. According to ATT&CK framework domain T1499, this vulnerability directly maps to the "Endpoint Denial of Service" technique, where adversaries target network infrastructure devices to cause service disruption.
Organizations affected by this vulnerability should immediately implement mitigation strategies focusing on network segmentation and access control measures. The most effective immediate solution involves deploying access control lists or firewall rules to filter out malformed IPv6 packets at network boundaries, particularly those containing extension headers. Cisco recommends applying the relevant software patches and updates as soon as they become available, which typically involve enhanced input validation routines and improved packet processing logic. Network administrators should also consider implementing monitoring solutions that can detect unusual line-card reload patterns and alert security teams to potential exploitation attempts. The vulnerability highlights the importance of maintaining current security patches and following vendor security advisories, as it represents a failure in the initial software validation process that could have been prevented through proper input sanitization and defensive programming practices.