CVE-2025-20155 is a vulnerability in the bootstrap loading process of Cisco IOS XE Software, specifically when devices are deployed in SD-WAN mode or configured with SD-Routing. The root cause is insufficient input validation of the bootstrap file, which is read by the system software during initial device setup. An attacker with authenticated local access and high privileges can exploit this by modifying a bootstrap file generated by Cisco Catalyst SD-WAN Manager and loading it into the device's flash memory. Upon device reload or configuration, the malicious bootstrap file can trigger arbitrary file writes to the underlying operating system. This can lead to unauthorized modification of system files, potentially allowing privilege escalation, persistence, or further compromise of the device. The vulnerability affects numerous IOS XE versions from 17.9.4 through 17.14.1a and related subversions, indicating a broad impact across Cisco's IOS XE product line. The CVSS v3.1 base score is 6.0, reflecting medium severity with high impact on confidentiality and integrity but no impact on availability. Exploitation requires local authenticated access with high privileges, no user interaction, and the scope is unchanged. No public exploits are known at this time, but the vulnerability poses a significant risk in environments where SD-WAN or SD-Routing is used and device management access is not tightly controlled.

The vulnerability allows an authenticated local attacker with high privileges to write arbitrary files to the operating system of Cisco IOS XE devices. This can compromise the confidentiality and integrity of the system by enabling unauthorized modification or insertion of malicious files, potentially leading to privilege escalation or persistent backdoors. While availability is not directly impacted, the integrity breach could indirectly affect device stability or network operations. Organizations relying on Cisco IOS XE for SD-WAN or SD-Routing deployments—common in enterprise and service provider networks—face risks of device compromise, data leakage, and disruption of critical network services. The broad range of affected versions increases the attack surface. Given the requirement for local authenticated access, the threat is more relevant in environments where internal access controls are weak or where attackers have already gained footholds. The absence of known exploits limits immediate risk but does not preclude future active exploitation.

To mitigate this vulnerability, organizations should: 1) Apply Cisco's security patches or software updates for affected IOS XE versions as soon as they become available. 2) Restrict and tightly control local administrative access to devices, ensuring only trusted personnel have high privilege accounts. 3) Implement strong authentication mechanisms, such as multi-factor authentication, for device management interfaces. 4) Monitor and audit bootstrap files generated by Cisco Catalyst SD-WAN Manager for unauthorized modifications before deployment. 5) Use network segmentation to limit access to device management networks, reducing the risk of unauthorized local access. 6) Employ integrity verification mechanisms on bootstrap files and device flash storage to detect tampering. 7) Maintain up-to-date inventories of affected devices and versions to prioritize remediation efforts. 8) Consider disabling SD-WAN or SD-Routing features if not in use, to reduce attack surface. 9) Regularly review and update security policies around device provisioning and configuration management to prevent unauthorized bootstrap file loading.