CVE-2021-1136 in IOS XR
Summary
by MITRE • 02/05/2021
Multiple vulnerabilities in Cisco Network Convergence System (NCS) 540 Series Routers, only when running Cisco IOS XR NCS540L software images, and Cisco IOS XR Software for the Cisco 8000 Series Routers could allow an authenticated, local attacker to execute unsigned code during the boot process on an affected device. For more information about these vulnerabilities, see the Details section of this advisory.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 02/24/2021
The vulnerability identified as CVE-2021-1136 represents a critical security flaw affecting Cisco Network Convergence System 540 Series Routers and Cisco 8000 Series Routers when operating specific IOS XR software versions. This vulnerability resides in the boot process of affected devices, creating a window of opportunity for authenticated local attackers to execute unsigned code. The flaw specifically impacts systems running Cisco IOS XR NCS540L software images and Cisco IOS XR Software for the Cisco 8000 Series Routers, making it particularly concerning for enterprise network infrastructure deployments. The vulnerability's exploitation potential is heightened by its location within the boot process, which occurs before normal security mechanisms are fully operational.
The technical nature of this vulnerability stems from insufficient code validation and integrity checking during the device boot sequence. An authenticated attacker with local access can leverage this weakness to inject and execute unsigned code, effectively bypassing normal security controls that would typically prevent unauthorized code execution. This represents a significant bypass of standard security measures, as the attacker does not require network access or complex remote exploitation techniques. The vulnerability's classification aligns with CWE-88, which addresses the injection of code during system boot or initialization processes. The flaw essentially creates an untrusted code execution path that operates outside the normal software integrity verification mechanisms, allowing malicious code to run with elevated privileges during the critical boot phase.
The operational impact of CVE-2021-1136 is severe and far-reaching for affected organizations. Successful exploitation could enable attackers to gain complete control over the affected routers, potentially leading to complete network compromise and disruption of critical infrastructure services. The local authentication requirement means that attackers must first obtain legitimate credentials, but this access requirement is often achievable through various social engineering or credential compromise techniques. Once exploited, the vulnerability could allow attackers to modify routing tables, intercept network traffic, create backdoors, or establish persistent access points within the network. The boot-time exploitation vector makes detection particularly challenging since the malicious code execution occurs before normal logging and monitoring systems are fully operational, potentially allowing attackers to maintain stealth while establishing their presence.
Organizations should immediately implement mitigation strategies focusing on access control and system hardening measures. The primary recommendation involves restricting local administrative access to affected devices through strict authentication controls and limiting the number of users with local privileges. Network segmentation and monitoring solutions should be deployed to detect anomalous boot behavior or unauthorized code execution attempts. The vulnerability's alignment with ATT&CK technique T1059.001 for command and scripting interpreter demonstrates the potential for attackers to leverage this flaw for persistent access and lateral movement. Regular security assessments and vulnerability scanning should be conducted to identify affected systems, while patch management procedures should be prioritized for immediate remediation. Additionally, organizations should implement comprehensive logging and monitoring solutions that can detect unauthorized code execution during boot processes, as traditional network-based detection methods may not capture this specific threat vector.