CVE-2021-1432

Q: What is the severity of CVE-2021-1432?

CVE-2021-1432 has a CVSS score of 7.3 (HIGH). This vulnerability allows authenticated low-privileged users on Cisco IOS XE SD-WAN devices to execute arbitrary commands as root through command injection in the CLI. Attackers can escalate privileges from limited access to full system control. Only devices running vulnerable Cisco IOS XE SD-WAN software are affected.

7.3 HIGH

Remote Code Execution

📋 TL;DR

This vulnerability allows authenticated low-privileged users on Cisco IOS XE SD-WAN devices to execute arbitrary commands as root through command injection in the CLI. Attackers can escalate privileges from limited access to full system control. Only devices running vulnerable Cisco IOS XE SD-WAN software are affected.

💻 Affected Systems

Products:

Cisco IOS XE SD-WAN Software

Versions: Releases 16.12.x and 17.3.x prior to 16.12.4 and 17.3.3

Operating Systems: Cisco IOS XE

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects SD-WAN functionality within Cisco IOS XE. Requires CLI access with low-privileged user credentials.

📦 What is this software?

Ios Xe by Cisco

Cisco IOS XE is Cisco's modern network operating system running on enterprise routers, switches, and wireless controllers deployed across corporate networks, data centers, branch offices, and service provider infrastructure worldwide. As the evolution of Cisco IOS, IOS XE provides a Linux-based modu...

Learn more about Ios Xe →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete compromise of the SD-WAN device allowing attackers to intercept/modify network traffic, deploy persistent backdoors, pivot to other network segments, and disrupt critical network services.

🟠

Likely Case

Privilege escalation leading to unauthorized configuration changes, network reconnaissance, and potential lateral movement within the SD-WAN environment.

🟢

If Mitigated

Limited impact if proper access controls restrict low-privileged user access and network segmentation isolates SD-WAN management interfaces.

🌐 Internet-Facing: MEDIUM - While exploitation requires authentication, internet-facing management interfaces could be targeted if credentials are compromised.

🏢 Internal Only: HIGH - Internal attackers with legitimate low-privileged access can easily escalate to root privileges and compromise critical network infrastructure.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: LOW

Exploitation requires authenticated access but is straightforward once an attacker has valid low-privileged credentials. The vulnerability is in the CLI command parsing.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Cisco IOS XE SD-WAN Software Release 16.12.4 or 17.3.3 and later

Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxe-sdwarbcmdexec-sspOMUr3

Restart Required: Yes

Instructions:

1. Download the fixed software from Cisco Software Center. 2. Backup current configuration. 3. Upgrade to Release 16.12.4 or 17.3.3 or later. 4. Reboot the device. 5. Verify the upgrade completed successfully.

🔧 Temporary Workarounds

Restrict CLI Access

all

Limit CLI access to only trusted administrators and remove unnecessary low-privileged user accounts.

configure terminal
username [username] privilege 15
line vty 0 15
transport input ssh
access-class [ACL_NAME] in

Implement AAA Controls

all

Use AAA authentication with TACACS+/RADIUS to enforce strict access controls and command authorization.

aaa new-model
aaa authentication login default group tacacs+ local
aaa authorization exec default group tacacs+ local
aaa accounting exec default start-stop group tacacs+

🧯 If You Can't Patch

Implement strict network segmentation to isolate SD-WAN management interfaces from general user networks
Enable comprehensive logging and monitoring of all CLI access attempts and command execution

🔍 How to Verify

Check if Vulnerable:

Check IOS XE version: 'show version' and verify if running 16.12.x before 16.12.4 or 17.3.x before 17.3.3 with SD-WAN features enabled

Check Version:

show version | include Version

Verify Fix Applied:

After upgrade, run 'show version' to confirm version is 16.12.4, 17.3.3 or later

📡 Detection & Monitoring

Log Indicators:

Unusual CLI command sequences from low-privileged users
Multiple failed authentication attempts followed by successful login
Commands typically restricted to privileged users executed by low-privileged accounts

Network Indicators:

Unexpected SSH/Telnet connections to SD-WAN management interfaces
Anomalous outbound connections from SD-WAN devices

SIEM Query:

source="iosxe" AND (event_type="cli_command" AND user_privilege="low" AND command="*inject*" OR command="*exec*" OR command="*system*")

📊 Metadata

CVE ID: CVE-2021-1432

CVSS v3 Score: 7.3 (HIGH)

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

CWE: CWE-20

Published: March 24, 2021

Last Updated: November 21, 2024

📋 TL;DR

💻 Affected Systems

📦 What is this software?

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe by Cisco

Ios Xe Sd Wan by Cisco

⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Restrict CLI Access

Implement AAA Controls

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

🔗 Related Vulnerabilities