CVE-2021-34770

10.0 CRITICAL

Remote Code Execution Denial of Service

📋 TL;DR

This critical vulnerability in Cisco Catalyst 9000 wireless controllers allows unauthenticated remote attackers to execute arbitrary code with administrative privileges or cause denial of service by sending specially crafted CAPWAP packets. It affects Cisco IOS XE software on Catalyst 9000 Family Wireless Controllers. The vulnerability stems from a logic error in CAPWAP packet validation.

💻 Affected Systems

Products:

• Cisco Catalyst 9000 Family Wireless Controllers

Versions: Cisco IOS XE Software releases prior to 17.3.4, 17.6.3, and 17.7.1

Operating Systems: Cisco IOS XE

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects wireless controllers, not access points. Requires CAPWAP protocol to be enabled (default configuration).

📦 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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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 →

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

Remote unauthenticated attacker gains full administrative control of the wireless controller, enabling complete network compromise, data theft, and persistent access.

🟠

Likely Case

Attackers cause denial of service by crashing the controller, disrupting wireless network availability for connected access points and clients.

🟢

If Mitigated

With proper network segmentation and access controls, impact is limited to isolated wireless management network segments.

🌐 Internet-Facing: HIGH

🏢 Internal Only: HIGH

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

No public exploit code available, but vulnerability is trivial to exploit with basic networking knowledge and packet crafting tools.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Cisco IOS XE Software releases 17.3.4, 17.6.3, 17.7.1 or later

Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ewlc-capwap-rce-LYgj8Kf

Restart Required: Yes

Instructions:

1. Download appropriate fixed software version from Cisco Software Center. 2. Backup current configuration. 3. Install new software using standard IOS XE upgrade procedures. 4. Reboot device to complete installation.

🔧 Temporary Workarounds

Restrict CAPWAP Access

all

Implement access control lists to restrict CAPWAP traffic to trusted management networks only

Copy

access-list 100 permit udp <trusted-network> <trusted-mask> host <controller-ip> eq 5246
access-list 100 deny udp any host <controller-ip> eq 5246
interface <management-interface>
ip access-group 100 in

🧯 If You Can't Patch

• Segment wireless management network and restrict access to CAPWAP port 5246/UDP using firewall rules
• Monitor for anomalous CAPWAP traffic patterns and implement intrusion detection/prevention systems

🔍 How to Verify

Check if Vulnerable:

Copy

Check IOS XE version: 'show version' and compare to affected releases (prior to 17.3.4, 17.6.3, 17.7.1)

Check Version:

Copy

show version | include Version

Verify Fix Applied:

Copy

Verify running version is 17.3.4, 17.6.3, 17.7.1 or later using 'show version' command

📡 Detection & Monitoring

Log Indicators:

• Unexpected device reloads/crashes
• CAPWAP protocol errors in system logs
• Authentication failures from unexpected sources

Network Indicators:

• Unusual CAPWAP traffic patterns to port 5246/UDP
• Malformed CAPWAP packets from untrusted sources
• Spike in CAPWAP protocol errors

SIEM Query:

Copy

source_port:5246 AND (packet_size:>1500 OR protocol_anomaly:true)

📊 Metadata

CVE ID: CVE-2021-34770

CVSS v3 Score: 10.0 (CRITICAL)

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

CWE: CWE-122

Published: September 23, 2021

Last Updated: October 30, 2025

🔗 References

• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ewlc-capwap-rce-LYgj8Kf Vendor Advisory
• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ewlc-capwap-rce-LYgj8Kf Vendor Advisory

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