CVE-2023-20190 in IOS XR
Summary
by MITRE • 09/13/2023
A vulnerability in the classic access control list (ACL) compression feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to bypass the protection that is offered by a configured ACL on an affected device.
This vulnerability is due to incorrect destination address range encoding in the compression module of an ACL that is applied to an interface of an affected device. An attacker could exploit this vulnerability by sending traffic through the affected device that should be denied by the configured ACL. A successful exploit could allow the attacker to bypass configured ACL protections on the affected device, allowing the attacker to access trusted networks that the device might be protecting.
There are workarounds that address this vulnerability.
This advisory is part of the September 2023 release of the Cisco IOS XR Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2023 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication .
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Analysis
by VulDB Data Team • 10/11/2023
The vulnerability identified as CVE-2023-20190 resides within the classic access control list compression feature of Cisco IOS XR Software, representing a critical weakness in network device security architecture. This flaw specifically impacts the destination address range encoding mechanism within the ACL compression module, creating a pathway for unauthorized network access that bypasses fundamental security controls. The vulnerability affects devices where ACLs are applied to interfaces, potentially allowing attackers to circumvent network segmentation and access protected internal networks. The issue stems from improper handling of address ranges during the compression process, which fundamentally undermines the integrity of access control policies that administrators rely upon to protect their network infrastructure.
The technical implementation of this vulnerability manifests through incorrect destination address range encoding within the ACL compression module, which operates under the purview of CWE-284 Access Control Bypass. When an attacker crafts specific traffic patterns that exploit this encoding flaw, the system fails to properly evaluate destination addresses against configured ACL rules. This misinterpretation occurs during the compression phase of ACL processing, where the software incorrectly handles address range representations, allowing traffic that should be denied to pass through the device. The vulnerability is particularly concerning because it operates at the network layer, affecting routing and forwarding decisions without requiring authentication credentials. The compression algorithm's failure to properly validate address ranges creates a condition where malicious packets can traverse network boundaries that should be protected by ACL policies, effectively nullifying the security controls established by network administrators.
The operational impact of CVE-2023-20190 extends beyond simple network access bypass to potentially enable broader network reconnaissance and lateral movement attacks. An unauthenticated remote attacker can leverage this vulnerability to access trusted network segments that should remain protected by configured ACLs, creating opportunities for data exfiltration, system compromise, and network disruption. The vulnerability's remote exploitation capability means that attackers do not require physical access or network credentials to exploit the flaw, making it particularly dangerous in environments where network devices serve as critical security boundaries. Organizations may experience unauthorized access to sensitive network resources, potential data breaches, and disruption of network services as attackers exploit the bypass mechanism to reach protected systems. This vulnerability directly impacts the CIA triad by compromising confidentiality through unauthorized data access and integrity through potential system compromise, while availability may suffer through network disruption caused by exploitation attempts.
Cisco has released a comprehensive security advisory addressing this vulnerability as part of its September 2023 IOS XR Software Security Advisory Bundled Publication, providing detailed mitigation guidance and firmware updates. The recommended remediation involves applying the latest software patches that correct the address range encoding logic within the ACL compression module, effectively closing the access control bypass mechanism. Network administrators should prioritize patching affected devices and implement temporary workarounds that involve disabling ACL compression features or implementing additional security controls. The vulnerability's classification under ATT&CK framework category T1046 Network Service Scanning and T1566 Phishing demonstrates the potential for attackers to use this flaw as part of broader attack chains, particularly in scenarios where network segmentation is critical for security posture. Organizations should conduct thorough vulnerability assessments to identify affected devices and implement monitoring solutions to detect exploitation attempts, as the vulnerability operates silently without generating standard security alerts. The combination of remote exploitability and the fundamental nature of access control bypass makes this vulnerability particularly severe in enterprise and critical infrastructure environments where network security boundaries are paramount for maintaining operational security and compliance with regulatory requirements.