CVE-2024-20398: Cisco IOS XR Privilege Escalation Flaw

CVE-2024-20398 Overview

A vulnerability in the command-line interface (CLI) of Cisco IOS XR Software could allow an authenticated, local attacker to obtain read/write file system access on the underlying operating system of an affected device. This vulnerability enables attackers with low-privileged accounts to elevate privileges to root through crafted CLI commands.

This vulnerability is classified as CWE-78 (OS Command Injection) and affects a wide range of Cisco IOS XR versions across the 6.x, 7.x, and 24.x release trains. The flaw stems from insufficient validation of user arguments passed to specific CLI commands, creating a pathway for privilege escalation attacks.

Critical Impact

Successful exploitation allows a low-privileged local attacker to elevate privileges to root, gaining complete read/write access to the underlying operating system file system on affected Cisco network devices.

Affected Products

• Cisco IOS XR versions 6.5.1 through 6.6.25
• Cisco IOS XR versions 7.0.0 through 7.11.2
• Cisco IOS XR version 24.1.1

Discovery Timeline

• September 11, 2024 - CVE-2024-20398 published to NVD
• October 3, 2024 - Last updated in NVD database

Technical Details for CVE-2024-20398

Vulnerability Analysis

This command injection vulnerability exists within the CLI subsystem of Cisco IOS XR Software. The vulnerability allows authenticated users with limited privileges to bypass security boundaries and execute commands with root-level access. The attack does not require user interaction and can be executed with low complexity once an attacker has authenticated access to the device CLI.

The exploitation of this vulnerability results in a complete compromise of the confidentiality, integrity, and availability of the affected system. An attacker can read sensitive configuration files, modify system settings, install persistent backdoors, or disrupt network operations entirely.

Root Cause

The root cause of CVE-2024-20398 is insufficient validation of user-supplied arguments passed to specific CLI commands within Cisco IOS XR Software. When processing certain commands, the CLI interpreter fails to properly sanitize or validate input parameters, allowing specially crafted arguments to be interpreted as system commands. This improper input validation enables attackers to inject arbitrary OS commands that execute with elevated privileges.

Attack Vector

The attack vector for this vulnerability requires local access to the device CLI. An attacker must first authenticate to the target device with a low-privileged account. Once authenticated, the attacker can craft malicious arguments for specific CLI commands that exploit the input validation weakness.

The attack flow typically proceeds as follows:

1. Attacker gains authenticated access to the Cisco IOS XR device CLI with a low-privileged user account
2. Attacker identifies vulnerable CLI commands that accept user-controlled arguments
3. Attacker crafts malicious input containing OS command injection payloads
4. The CLI interpreter fails to properly validate the input and passes it to the underlying operating system
5. Injected commands execute with root privileges, granting full system access

Detection Methods for CVE-2024-20398

Indicators of Compromise

• Unexpected privilege escalation events in system logs where low-privileged users gain root access
• Unusual CLI command patterns containing special characters or command separators (;, |, &&, etc.)
• Unauthorized modifications to system files or configurations
• New or unexpected user accounts with elevated privileges

Detection Strategies

• Monitor authentication logs for low-privileged accounts executing administrative functions
• Implement alerting on CLI sessions that spawn unexpected child processes or access restricted file paths
• Review syslog entries for command execution anomalies or privilege escalation attempts
• Deploy network behavior analysis to detect unusual command patterns from authenticated sessions

Monitoring Recommendations

• Enable comprehensive CLI command logging on all Cisco IOS XR devices
• Configure TACACS+ or RADIUS accounting to capture detailed command histories
• Implement centralized log collection and analysis for all network infrastructure devices
• Establish baseline behavioral patterns for privileged command usage and alert on deviations

How to Mitigate CVE-2024-20398

Immediate Actions Required

• Review and restrict CLI access to only essential personnel with a business need
• Implement role-based access control (RBAC) to limit commands available to low-privileged users
• Audit all user accounts on affected devices and remove unnecessary accounts
• Apply patches from Cisco as soon as they are available for your software version

Patch Information

Cisco has released security updates to address this vulnerability. Administrators should consult the Cisco Security Advisory for detailed information on fixed software releases and upgrade paths for affected versions. The advisory provides specific fixed release information for each affected IOS XR version train.

Organizations should prioritize upgrading to a fixed software release that addresses CVE-2024-20398. Given the wide range of affected versions from 6.5.1 through 24.1.1, careful planning is required to identify the appropriate upgrade path for each deployment.

Workarounds

• Restrict local CLI access to trusted administrators only and implement strong authentication mechanisms
• Use AAA (Authentication, Authorization, and Accounting) servers to enforce granular command authorization policies
• Implement network segmentation to limit which systems can access device management interfaces
• Enable command authorization to restrict which commands can be executed by non-privileged users

# Example AAA configuration to restrict CLI command authorization
aaa authorization exec default group tacacs+ local
aaa authorization commands 15 default group tacacs+ local
aaa accounting commands 15 default start-stop group tacacs+