CVE-2020-3449 in IOS XR
Summary
by MITRE
A vulnerability in the Border Gateway Protocol (BGP) additional paths feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to prevent authorized users from monitoring the BGP status and cause the BGP process to stop processing new updates, resulting in a denial of service (DOS) condition. The vulnerability is due to an incorrect calculation of lexicographical order when displaying additional path information within Cisco IOS XR Software, which causes an infinite loop. An attacker could exploit this vulnerability by sending a specific BGP update from a BGP neighbor peer session of an affected device; an authorized user must then issue a show bgp command for the vulnerability to be exploited. A successful exploit could allow the attacker to prevent authorized users from properly monitoring the BGP status and prevent BGP from processing new updates, resulting in outdated information in the routing and forwarding tables.
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Analysis
by VulDB Data Team • 11/10/2020
The vulnerability identified as CVE-2020-3449 resides within the Border Gateway Protocol implementation of Cisco IOS XR Software, specifically affecting the additional paths feature that enables multiple paths to be advertised for the same destination. This weakness represents a critical security flaw that undermines the stability and reliability of network infrastructure by creating a denial of service condition through improper handling of BGP update messages. The issue manifests when the software encounters specific BGP updates containing additional path information that triggers an incorrect lexicographical ordering calculation, ultimately leading to a system hang or crash.
The technical root cause of this vulnerability stems from a flawed implementation in how Cisco IOS XR Software processes additional path information within BGP updates. When a malicious actor sends a crafted BGP update message containing specific path attributes, the system's internal lexicographical ordering algorithm enters an infinite loop due to improper boundary condition handling. This computational flaw occurs during the processing of BGP additional paths, where the software fails to properly validate or handle certain path attribute combinations that would normally be processed without issue. The vulnerability is particularly insidious because it requires minimal authentication and can be exploited remotely through a standard BGP peer session, making it accessible to any attacker with network connectivity to the affected device.
The operational impact of CVE-2020-3449 extends far beyond simple service disruption, as it fundamentally compromises the network's ability to maintain accurate routing information and process new BGP updates effectively. Authorized network operators face significant challenges when attempting to monitor BGP status through standard show bgp commands, as these operations trigger the exploitable code path and cause the BGP process to become unresponsive. The resulting denial of service condition leads to outdated routing tables and potential traffic black holes, where network traffic may be routed through suboptimal paths or completely fail to reach intended destinations. This vulnerability directly affects network availability and can cause cascading failures throughout the internet infrastructure, particularly in core network equipment where IOS XR software is deployed.
Network security professionals should recognize this vulnerability as a prime example of a software defect that can be exploited through protocol manipulation, aligning with ATT&CK technique T1210 for exploitation of remote services and CWE-835 for infinite loops or iteration limits. The vulnerability demonstrates how seemingly minor implementation flaws in network protocol handling can result in catastrophic service disruption. Organizations should implement immediate mitigations including disabling the additional paths feature when not required, applying Cisco's security patches, and monitoring BGP peer sessions for anomalous update patterns. Network segmentation and access controls should be strengthened to limit potential attack vectors, while regular network health monitoring should include verification of BGP process stability and routing table consistency to detect exploitation attempts. The vulnerability highlights the importance of thorough protocol implementation testing and the need for robust error handling in critical network infrastructure software to prevent such exploitation scenarios.