CVE-2025-20338: Cisco IOS XE CLI Command Injection RCE

CVE-2025-20338 Overview

CVE-2025-20338 is an argument injection vulnerability in the command-line interface (CLI) of Cisco IOS XE Software. An authenticated attacker with privilege level 15 administrative credentials can execute arbitrary commands as root on the underlying operating system. The flaw stems from insufficient validation of user-supplied arguments passed to specific CLI commands. Exploitation requires local CLI access and valid administrative credentials, which limits the attacker population but enables a full escape from the restricted IOS XE shell to the Linux host. The vulnerability is tracked under CWE-141: Improper Neutralization of Parameter/Argument Delimiters.

Critical Impact

A level 15 administrator can break out of the IOS XE CLI sandbox and run arbitrary commands as root on the underlying Linux operating system, giving full control of the network device.

Affected Products

• Cisco IOS XE Software 3.x releases (3.5 through 3.18 trains)
• Cisco IOS XE Software 16.x releases (16.6 through 16.12 trains)
• Cisco IOS XE Software 17.x releases (17.1 through 17.16 trains)

Discovery Timeline

• 2025-09-24 - CVE-2025-20338 published to the National Vulnerability Database
• 2026-09-26 - Last updated in NVD database

Technical Details for CVE-2025-20338

Vulnerability Analysis

Cisco IOS XE runs a Linux-based control plane that executes the IOSd process alongside other daemons. Administrators normally interact with the device through a restricted CLI that abstracts the underlying operating system. CVE-2025-20338 breaks this separation. Specific CLI commands do not properly neutralize parameter and argument delimiters before passing user input into downstream system calls. An attacker with level 15 privileges can craft arguments that are reinterpreted by the shell layer beneath the CLI parser. The result is arbitrary command execution with root privileges on the host operating system. Because IOS XE devices routinely terminate management, routing, and segmentation boundaries, root access on the control plane allows persistent implants, configuration tampering, and lateral access to adjacent management networks.

Root Cause

The root cause is improper neutralization of argument delimiters, classified as CWE-141. The affected CLI commands concatenate attacker-controlled strings into argument lists executed by the underlying operating system without sanitizing delimiter characters. This permits argument injection that alters the intended command structure and introduces attacker-chosen operations.

Attack Vector

The attacker must authenticate locally to the device CLI using valid level 15 administrative credentials. From the CLI prompt, the attacker invokes one of the vulnerable commands with crafted arguments that inject additional parameters or shell operations. The injected content is processed by the underlying operating system as root, bypassing the role-based access controls that normally constrain even privileged IOS XE users to a defined command set. Exploitation does not require user interaction and does not cross a trust boundary beyond the device itself.

See the Cisco Security Advisory for the authoritative list of affected commands and fixed releases.

Detection Methods for CVE-2025-20338

Indicators of Compromise

• Unexpected processes spawned by IOSd or CLI helper daemons running as root outside of normal operational patterns.
• CLI accounting or TACACS+ logs showing level 15 users invoking the affected commands with unusual argument strings containing shell metacharacters.
• New or modified files in writable filesystem locations (for example, bootflash: or /tmp) that do not correspond to authorized changes.
• Unexplained outbound connections initiated from the device management interface.

Detection Strategies

• Enable AAA command accounting for privilege level 15 and forward records to a central log store for inspection of argument patterns.
• Baseline the set of CLI commands used by operations teams and alert on invocations containing delimiter characters such as ;, |, backticks, or $().
• Compare running configuration and startup configuration hashes against a known-good baseline on a scheduled interval.

Monitoring Recommendations

• Forward syslog, AAA accounting, and NETCONF/RESTCONF audit records from all IOS XE devices to a centralized SIEM.
• Monitor administrative sessions for anomalous command sequences and off-hours privilege level 15 activity.
• Correlate device-sourced network flows with expected management plane behavior and alert on deviations.

How to Mitigate CVE-2025-20338

Immediate Actions Required

• Review the Cisco Security Advisory cisco-sa-iosxe-arg-inject-EyDDbh4e and identify affected devices across the IOS XE 3.x, 16.x, and 17.x trains.
• Schedule and apply the fixed IOS XE release identified in the Cisco advisory for each affected platform.
• Audit all accounts holding privilege level 15 and remove or downgrade accounts that do not require full administrative access.
• Rotate credentials for any administrative account suspected of exposure, including local, TACACS+, and RADIUS-backed users.

Patch Information

Cisco has released fixed software addressing CVE-2025-20338. Refer to the Fixed Software section of the Cisco Security Advisory for the minimum patched release that corresponds to each affected IOS XE train. No workarounds that fully address the vulnerability are listed by the vendor; patching is the required remediation.

Workarounds

• Restrict device CLI access to a minimal set of trusted administrators and enforce multi-factor authentication for jump hosts used to reach IOS XE devices.
• Enforce role-based CLI views and command authorization through TACACS+ to limit which commands level 15 users can invoke.
• Isolate device management interfaces on a dedicated out-of-band network with strict access control lists.
• Enable command accounting and ship records off-device so administrative activity remains auditable even if a device is compromised.

# Example: enable AAA command accounting for level 15 to a central TACACS+ server
aaa new-model
aaa authentication login default group tacacs+ local
aaa authorization commands 15 default group tacacs+ local
aaa accounting commands 15 default start-stop group tacacs+