CVE-2023-20135 in IOS XR
Summary
by MITRE • 09/13/2023
A vulnerability in Cisco IOS XR Software image verification checks could allow an authenticated, local attacker to execute arbitrary code on the underlying operating system.
This vulnerability is due to a time-of-check, time-of-use (TOCTOU) race condition when an install query regarding an ISO image is performed during an install operation that uses an ISO image. An attacker could exploit this vulnerability by modifying an ISO image and then carrying out install requests in parallel. A successful exploit could allow the attacker to execute arbitrary code on an affected device.
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Analysis
by VulDB Data Team • 10/11/2023
The vulnerability identified as CVE-2023-20135 represents a critical security flaw in Cisco IOS XR Software that stems from a time-of-check, time-of-use race condition during ISO image verification processes. This weakness specifically manifests when the system performs install operations using ISO images, creating an exploitable window where an authenticated local attacker can manipulate the system's behavior through carefully orchestrated parallel installation requests. The vulnerability resides in the software's image verification mechanisms, which fail to maintain consistent state validation throughout the installation process, allowing malicious actors to bypass intended security controls.
The technical implementation of this vulnerability follows a classic TOCTOU pattern where the system initially checks the integrity of an ISO image and then subsequently uses that same image without revalidating its state. During the window between these two operations, an attacker can modify the ISO image on disk while the installation process is in progress, causing the system to execute code contained within the modified image rather than the originally intended software. This race condition occurs at the operating system level within the IOS XR software stack, specifically affecting the installation and verification routines that govern how ISO images are processed and validated. The flaw is particularly dangerous because it requires only local authentication privileges, making it accessible to anyone with legitimate access to the device's administrative interfaces.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with elevated privileges on the underlying operating system and potentially enables further exploitation within the network infrastructure. Successful exploitation could lead to complete system compromise, allowing attackers to modify system configurations, install backdoors, or exfiltrate sensitive operational data from network devices that rely on IOS XR software. The vulnerability affects Cisco IOS XR devices running specific software versions, creating a significant risk for network infrastructure administrators who may not have immediate visibility into which devices are impacted. This weakness essentially undermines the integrity of the software installation process and can result in persistent threats that are difficult to detect and remediate.
Organizations should implement immediate mitigations including applying the latest Cisco security patches and updates that address the TOCTOU race condition in the image verification process. Network administrators should also consider implementing additional access controls and monitoring mechanisms to detect unauthorized installation activities, particularly parallel installation requests that could indicate exploitation attempts. The vulnerability aligns with CWE-367, which describes the Time-of-Check to Time-of-Use race condition, and represents a significant concern from an ATT&CK perspective under the T1059.001 technique for Command and Scripting Interpreter. Additionally, implementing proper audit logging of installation operations and establishing baseline monitoring for unusual parallel processing patterns can help detect exploitation attempts before they succeed. Regular security assessments of network device software configurations and maintaining up-to-date vulnerability management processes are essential for preventing exploitation of this and similar race condition vulnerabilities.