CVE-2025-20181: Cisco IOS Software RCE Vulnerability

CVE-2025-20181 Overview

CVE-2025-20181 is a secure boot bypass vulnerability in Cisco IOS Software for Catalyst 2960X, 2960XR, 2960CX, and 3560CX Series Switches. The flaw stems from missing signature verification [CWE-347] for specific files loaded during the device boot process. An authenticated local attacker with privilege level 15, or an unauthenticated attacker with physical access, can place a crafted file into a specific location to execute persistent code at boot time. Successful exploitation breaks the chain of trust that anchors the platform's secure boot process. Cisco raised the Security Impact Rating (SIR) of this advisory from Medium to High because the flaw defeats a major device security feature.

Critical Impact
Attackers who exploit CVE-2025-20181 can execute arbitrary, persistent code at boot time, undermining the switch's chain of trust and gaining a foothold that survives reboots and image reinstallation.

Affected Products

Cisco Catalyst 2960X and 2960XR Series Switches running vulnerable Cisco IOS releases
Cisco Catalyst 2960CX Series Switches running vulnerable Cisco IOS releases
Cisco Catalyst 3560CX Series Switches running vulnerable Cisco IOS releases

Discovery Timeline

2025-05-07 - CVE-2025-20181 published to the National Vulnerability Database
2025-05-07 - Cisco publishes security advisory cisco-sa-c2960-3560-sboot-ZtqADrHq
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-20181

Vulnerability Analysis

The vulnerability defeats the secure boot process on affected Catalyst switches. Cisco IOS loads specific files during boot without validating their cryptographic signatures. Because the boot loader trusts these files implicitly, an attacker who can place a crafted file at the expected location controls code that runs before the operating system enforces its security boundaries. This grants persistence at the lowest software layer available on the device and effectively breaks the chain of trust that anchors runtime integrity guarantees.

The issue is classified as CWE-347: Improper Verification of Cryptographic Signature. The attack requires either privilege level 15 (the highest Cisco IOS privilege, equivalent to enable mode with full command access) or physical access to the switch, which limits the exploitability window in well-controlled environments. However, network switches deployed in wiring closets, remote branches, or shared facilities frequently lack strong physical controls.

Root Cause

The root cause is missing signature verification for files consumed during the boot sequence. Secure boot is intended to validate every stage of the boot chain against a trusted signing key. In the affected IOS builds, one or more files that influence boot execution are loaded without this signature check, allowing substitution with attacker-controlled content.

Attack Vector

An authenticated attacker with privilege 15 can write the crafted file to the target location on the device file system using standard IOS commands. Alternatively, an attacker with physical access can mount the storage medium or use console-level recovery paths to place the file. On the next reboot, the modified content is loaded and executed, installing a persistent implant that survives IOS upgrades and configuration resets.

No verified public exploit code or proof-of-concept has been published. Refer to the Cisco Security Advisory for the authoritative technical description.

Detection Methods for CVE-2025-20181

Indicators of Compromise

Unexpected files or unauthorized modifications in the switch flash file system, particularly in boot-related paths
Unexpected changes to the boot variable (boot system configuration) or bootloader parameters
Unexplained reboots followed by anomalous device behavior, memory usage, or process activity
Console or logging output showing boot-time messages that do not match the installed IOS image

Detection Strategies

Compare the output of show flash: and verify /md5 against a known-good baseline to identify unauthorized files
Monitor privilege-15 command usage, especially copy, write, and file-system operations targeting boot locations
Review AAA and TACACS+ logs for unusual privilege-15 sessions, out-of-hours access, or logins from unexpected sources
Validate device image and boot integrity using Cisco IOS image verification and platform-level Secure Boot status commands where supported

Monitoring Recommendations

Forward switch syslog and AAA authentication events to a centralized SIEM for correlation of privileged access and reboots
Alert on any change to boot variables, startup configuration files, or the contents of flash boot directories
Track physical access to network closets housing Catalyst 2960 and 3560CX switches using badge and camera systems

How to Mitigate CVE-2025-20181

Immediate Actions Required

Apply the fixed Cisco IOS release identified in the Cisco Security Advisory cisco-sa-c2960-3560-sboot-ZtqADrHq for each affected Catalyst 2960 and 3560CX model
Restrict privilege level 15 accounts to a minimum set of administrators and enforce strong authentication, ideally via TACACS+ or RADIUS with MFA at the jump host
Enforce strict physical security controls for all affected switches, including locked cabinets and controlled console port access
Audit switch flash contents against a known-good baseline and re-image any device suspected of tampering

Patch Information

Cisco has published the security advisory cisco-sa-c2960-3560-sboot-ZtqADrHq with fixed software information. Administrators should consult the advisory for the specific IOS train and release that addresses CVE-2025-20181 on their platform, then plan an upgrade window. No workaround fully replaces the fixed software.

Workarounds

No software workaround is available from Cisco; upgrading to a fixed release is required
Reduce risk by tightening privilege-15 access, disabling unused management interfaces, and requiring console authentication
Enclose affected switches in locked physical enclosures and disable USB console ports where operationally feasible