CVE-2023-20191 in IOS XR
Summary
by MITRE • 09/13/2023
A vulnerability in the access control list (ACL) processing on MPLS interfaces in the ingress direction of Cisco IOS XR Software could allow an unauthenticated, remote attacker to bypass a configured ACL.
This vulnerability is due to incomplete support for this feature. An attacker could exploit this vulnerability by attempting to send traffic through an affected device. A successful exploit could allow the attacker to bypass an ACL on the affected device.
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
This vulnerability exists within the access control list processing functionality of Cisco IOS XR Software operating on multiprotocol label switching interfaces in the ingress direction. The flaw represents a critical access control bypass issue that undermines the security posture of network devices running affected software versions. The vulnerability stems from incomplete implementation of ACL processing features specifically designed for MPLS traffic handling, creating a security gap that allows unauthorized network access. According to the Cisco security advisory, this issue affects devices where MPLS interfaces are configured with access control lists, potentially enabling attackers to circumvent network security policies that should restrict traffic flow.
The technical exploitation of this vulnerability occurs through remote, unauthenticated attack vectors targeting the ingress processing of MPLS traffic on affected Cisco IOS XR devices. Attackers can craft specific traffic patterns that exploit the incomplete ACL support mechanism, effectively allowing them to bypass configured access control rules. This flaw operates at the network layer where MPLS packets are processed, enabling attackers to traverse network boundaries that should be protected by ACL configurations. The vulnerability manifests when the device processes incoming MPLS traffic through interfaces where access control lists have been applied, creating a pathway for unauthorized traffic to pass through the network perimeter. This represents a fundamental failure in the software's security model where the expected behavior of ACL enforcement is not properly implemented for MPLS ingress processing.
The operational impact of this vulnerability extends beyond simple network access bypass, potentially compromising the integrity of network security policies and exposing sensitive network segments to unauthorized access. Organizations relying on Cisco IOS XR devices for network segmentation and traffic control may experience significant security degradation, as attackers could bypass configured security controls without authentication. This vulnerability affects network infrastructure that depends on MPLS for traffic engineering and quality of service management, potentially allowing malicious actors to access critical network resources, perform reconnaissance activities, or conduct further attacks within the compromised network environment. The implications are particularly severe for organizations using MPLS-based networks where security policies are enforced through access control lists on ingress interfaces.
Mitigation strategies for this vulnerability include implementing the workarounds provided by Cisco in their security advisory, which typically involve temporary configuration changes or operational procedures to prevent exploitation. Network administrators should immediately review their MPLS interface configurations and assess whether access control lists are properly implemented on ingress paths. The recommended approach involves applying Cisco's published patches and configuration updates as part of the September 2023 security advisory bundle. Additionally, organizations should consider implementing network segmentation strategies and monitoring for anomalous traffic patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-284 Access Control Bypass and potentially maps to ATT&CK technique T1071.004 Application Layer Protocol: DNS, as attackers may leverage this bypass to conduct reconnaissance or establish command and control communications. Network security teams should also implement enhanced monitoring for traffic that bypasses expected ACL rules and maintain updated threat intelligence feeds to detect potential exploitation attempts.