CVE-2019-1849 in IOS XR
Summary
by MITRE
A vulnerability in the Border Gateway Patrol (BGP) Multiprotocol Label Switching (MPLS)-based Ethernet VPN (EVPN) implementation of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to trigger a denial of service (DoS) condition on an affected device. The vulnerability is due to a logic error that occurs when the affected software processes specific EVPN routing information. An attacker could exploit this vulnerability by injecting malicious traffic patterns into the targeted EVPN network. A successful exploit could result in a crash of the l2vpn_mgr process on Provider Edge (PE) device members of the same EVPN instance (EVI). On each of the affected devices, a crash could lead to system instability and the inability to process or forward traffic through the device, resulting in a DoS condition that would require manual intervention to restore normal operating conditions.
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Analysis
by VulDB Data Team • 09/21/2023
The vulnerability described in CVE-2019-1849 represents a critical denial of service weakness within Cisco IOS XR Software's implementation of Border Gateway Protocol with Multiprotocol Label Switching based Ethernet VPN services. This flaw specifically affects Provider Edge devices that participate in the same EVPN instance, creating a pathway for adjacent attackers to disrupt network operations without requiring authentication credentials. The vulnerability stems from a fundamental logic error that manifests when the system processes certain EVPN routing information, particularly within the l2vpn_mgr process component that manages Layer 2 VPN services. This issue demonstrates how complex routing protocols can contain subtle implementation flaws that, when exploited, can cascade into complete service disruption.
The technical exploitation of this vulnerability occurs through the injection of carefully crafted traffic patterns into the targeted EVPN network infrastructure. Attackers leveraging this weakness can specifically target the l2vpn_mgr process on PE devices, causing it to crash and subsequently destabilizing the entire device's ability to maintain proper traffic forwarding operations. The vulnerability's impact extends beyond simple service interruption as it affects the core routing and switching functionality that underpins enterprise and service provider networks. When the l2vpn_mgr process fails, the device loses its capacity to properly handle Layer 2 VPN traffic, creating a cascading effect that can disrupt communications across the entire EVPN instance. This type of vulnerability aligns with CWE-843, which addresses the use of incorrect access control mechanisms, and represents a classic example of how protocol implementation flaws can lead to remote code execution or denial of service conditions.
The operational impact of CVE-2019-1849 creates significant challenges for network administrators and security operations teams who must maintain service availability for critical network infrastructure. Device crashes require manual intervention to restore normal operations, including system reboot procedures that can result in extended service outages and potential data loss during the recovery process. The requirement for manual restoration indicates that automated recovery mechanisms are insufficient to address this particular vulnerability, forcing operators to maintain emergency response procedures and potentially impacting customer service levels. Organizations relying on EVPN services for their network connectivity face heightened risk of service disruption, particularly in environments where network stability is paramount for business operations. This vulnerability's adjacency requirement means that attackers must be physically present within the network segment to exploit it, but this limitation does not mitigate the severity of impact on network availability and service continuity.
Mitigation strategies for this vulnerability should focus on implementing network segmentation controls to limit adjacent access to critical network infrastructure, along with regular software updates and patches provided by Cisco to address the underlying logic error. Network administrators should consider implementing monitoring solutions that can detect anomalous traffic patterns indicative of exploitation attempts, and establish automated alerting mechanisms to quickly identify when l2vpn_mgr processes begin to exhibit instability. The implementation of access control lists and traffic filtering rules can help reduce the attack surface by limiting which devices can inject traffic into the EVPN network. Additionally, organizations should conduct regular vulnerability assessments and penetration testing to identify potential exploitation vectors and ensure that their network defenses remain effective against known vulnerabilities. The remediation approach should align with ATT&CK framework's T1059.007 technique for command and control through remote services, as the vulnerability enables unauthorized remote disruption of network services without authentication, requiring defensive measures that address both network access controls and process-level protections.