CVE-2021-1243 in IOS XR
Summary
by MITRE • 02/05/2021
A vulnerability in the Local Packet Transport Services (LPTS) programming of the SNMP with the management plane protection feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to allow connections despite the management plane protection that is configured to deny access to the SNMP server of an affected device. This vulnerability is due to incorrect LPTS programming when using SNMP with management plane protection. An attacker could exploit this vulnerability by connecting to an affected device using SNMP. A successful exploit could allow the attacker to connect to the device on the configured SNMP ports. Valid credentials are required to execute any of the SNMP requests.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 02/24/2021
The vulnerability identified as CVE-2021-1243 resides within the Local Packet Transport Services implementation of Cisco IOS XR Software, specifically affecting the interaction between SNMP protocol handling and management plane protection mechanisms. This flaw represents a critical security weakness that undermines the fundamental security posture of network devices by allowing unauthorized access despite configured protections. The vulnerability manifests when the LPTS programming fails to properly enforce access controls when SNMP requests are processed through the management plane protection framework, creating an exploitable pathway for remote attackers to bypass security measures.
The technical root cause of this vulnerability stems from improper LPTS configuration handling when SNMP traffic is processed within the management plane protection context. According to CWE-284, this represents an improper access control vulnerability where the system fails to properly enforce authorization checks. The flaw occurs during the SNMP server connection processing phase, where the LPTS component does not correctly validate or enforce the management plane protection rules that should normally prevent unauthorized access to management interfaces. This misconfiguration allows an attacker to establish connections to SNMP ports even when the device is configured to deny such access through management plane protection mechanisms.
From an operational perspective, this vulnerability presents a significant risk to network infrastructure security as it enables remote attackers to gain unauthorized access to network devices without requiring valid credentials for the initial connection phase. While valid credentials are still required to execute SNMP requests, the ability to bypass the initial access control mechanisms creates a dangerous attack vector that could lead to full device compromise. The vulnerability affects Cisco IOS XR Software versions where management plane protection is enabled, making it particularly concerning for enterprise networks that rely on these security features for protecting critical infrastructure. Attackers could leverage this vulnerability to perform reconnaissance, gather system information, or potentially escalate privileges through subsequent exploitation attempts.
The impact of this vulnerability extends beyond simple unauthorized access as it undermines the trust model of network security controls. According to ATT&CK framework technique T1078, this vulnerability enables unauthorized access to network devices, while T1046 represents the network service scanning that could be performed once initial access is gained. Organizations with management plane protection enabled may believe their devices are secure against remote access attempts, but this vulnerability demonstrates how misconfigurations in underlying security components can create exploitable gaps. The vulnerability is particularly dangerous because it operates at the protocol level where management plane protection is designed to enforce access controls, making it difficult to detect through conventional network monitoring approaches.
Mitigation strategies for CVE-2021-1243 should focus on immediate software updates and configuration reviews. Cisco has released patches addressing this vulnerability in affected IOS XR Software versions, making patch management a critical first step for affected organizations. Network administrators should also implement additional monitoring controls to detect unusual SNMP access patterns and consider disabling SNMP if not essential for operations. The vulnerability highlights the importance of proper security configuration management and the need for regular security assessments of network infrastructure components. Organizations should review their management plane protection configurations to ensure that all security features are properly implemented and functioning as intended, particularly when integrating multiple security mechanisms like SNMP and LPTS. Additionally, implementing network segmentation and access control lists can provide additional defense-in-depth measures to limit potential exploitation impact.