CVE-2024-20456: Cisco IOS XR Privilege Escalation Flaw

CVE-2024-20456 Overview

A vulnerability in the boot process of Cisco IOS XR Software could allow an authenticated, local attacker with high privileges to bypass the Cisco Secure Boot functionality and load unverified software on an affected device. This Secure Boot Bypass vulnerability stems from an error in the software build process that permits manipulation of system configuration options to circumvent integrity checks performed during the booting process.

To exploit this vulnerability successfully, the attacker must already have root-system privileges on the affected device. A successful exploit could allow the attacker to control the boot configuration, enabling them to bypass the requirement to run Cisco signed images or alter the security properties of the running system.

Critical Impact

Successful exploitation allows attackers with root-system privileges to bypass Cisco Secure Boot protections, load unsigned or malicious software images, and alter the security properties of network infrastructure devices deployed in enterprise and service provider environments.

Affected Products

• Cisco IOS XR Software version 24.2.1
• Cisco 8000 Series Routers (8201, 8202, 8404, 8608, 8804, 8808, 8812, 8818, and related models)
• Cisco NCS 540 Series Routers (multiple variants including NCS 540-12Z20G, NCS 540-24Z8Q2C, NCS 540X series)
• Cisco NCS 1000 Series (NCS 1010, NCS 1014)
• Cisco NCS 5700 Series (NCS 57B1, NCS 57C1, NCS 57D2)

Discovery Timeline

• July 10, 2024 - CVE-2024-20456 published to NVD
• August 4, 2025 - Last updated in NVD database

Technical Details for CVE-2024-20456

Vulnerability Analysis

This vulnerability affects the Cisco Secure Boot implementation in IOS XR Software, a critical security feature designed to ensure that only cryptographically verified and Cisco-signed software images can be loaded during the device boot process. The flaw allows an attacker who has already obtained root-system privileges to manipulate boot configuration options in a way that bypasses the integrity verification mechanisms.

The vulnerability is classified under CWE-732 (Incorrect Permission Assignment for Critical Resource), indicating that the issue relates to how permissions and access controls are configured for boot-related resources. An attacker exploiting this vulnerability could load unsigned or modified firmware images, potentially enabling persistent compromise of the network device that survives reboots and standard recovery procedures.

The impact is significant for enterprise and service provider environments where Cisco 8000 Series and NCS routers serve as critical network infrastructure components. Compromised devices could be used to intercept traffic, pivot to other network segments, or maintain persistent unauthorized access.

Root Cause

The root cause of this vulnerability is an error in the software build process for Cisco IOS XR Software. This build-time defect resulted in incorrect permission assignments for critical boot configuration resources, allowing high-privileged users to modify parameters that should be protected by the Secure Boot chain of trust. The vulnerability enables manipulation of configuration options that control which integrity checks are performed during the boot sequence.

Attack Vector

The attack requires local access to the affected device and root-system privileges, which represents a significant barrier to exploitation but also indicates post-compromise persistence scenarios. An attacker who has already gained administrative control of a Cisco IOS XR device through other means could exploit this vulnerability to:

1. Modify boot configuration parameters to disable or bypass integrity verification
2. Load unsigned or tampered software images that would normally be rejected by Secure Boot
3. Alter security properties of the running system to weaken other protections
4. Establish persistent access that survives device reboots and standard remediation attempts

The exploitation flow involves manipulating system configuration options during or before the boot process to circumvent the cryptographic signature verification that Secure Boot normally enforces.

Detection Methods for CVE-2024-20456

Indicators of Compromise

• Unexpected changes to boot configuration files or parameters on Cisco IOS XR devices
• Presence of unsigned or non-Cisco software images in device storage
• Anomalous boot behavior or extended boot times indicating modified boot sequences
• Alerts from device integrity verification tools showing signature mismatches

Detection Strategies

• Implement regular auditing of boot configuration settings on affected Cisco devices using show secure boot and related commands
• Deploy file integrity monitoring on network device configurations to detect unauthorized changes
• Enable and monitor syslog messages related to boot processes and Secure Boot verification events
• Establish baseline boot behavior metrics and alert on deviations

Monitoring Recommendations

• Configure centralized logging for all Cisco IOS XR devices to capture boot-related events and configuration changes
• Implement privileged access monitoring to track root-system level command execution
• Schedule periodic secure boot status verification as part of network security assessments
• Monitor for privilege escalation attempts that could precede exploitation of this vulnerability

How to Mitigate CVE-2024-20456

Immediate Actions Required

• Review the Cisco Security Advisory for specific fixed software versions and upgrade guidance
• Audit all affected Cisco IOS XR devices for unauthorized configuration changes or suspicious boot configurations
• Verify current Secure Boot status on all affected platforms using Cisco IOS XR diagnostic commands
• Restrict root-system level access to essential personnel only and implement multi-factor authentication where possible
• Enable comprehensive logging and monitoring on affected devices pending software updates

Patch Information

Cisco has released security patches addressing this vulnerability. Organizations should consult the Cisco Security Advisory cisco-sa-xr-secure-boot-quD5g8Ap for detailed information on fixed software releases for their specific hardware platforms. Given the breadth of affected products across the Cisco 8000 Series and NCS portfolio, administrators should verify the appropriate fixed version for each device model in their environment.

Workarounds

• Implement strict access control policies limiting root-system level access to only trusted administrators with verified business requirements
• Enable console session logging and command authorization to maintain audit trails of privileged operations
• Deploy network segmentation to limit lateral movement potential from compromised devices
• Consider implementing out-of-band management networks to reduce attack surface exposure

# Verify Secure Boot status on Cisco IOS XR
show secure boot status

# Review boot configuration
show running-config | include boot

# Check software image signatures
admin show install active summary

# Enable configuration change logging
logging console informational
logging buffered 1000000 informational