CVE-2021-34727 – This vulnerability allows unauthenticated remot... (How to Fix)

Q: What is the severity of CVE-2021-34727?

CVE-2021-34727 has a CVSS score of 9.8 (CRITICAL). This vulnerability allows unauthenticated remote attackers to trigger a buffer overflow in Cisco IOS XE SD-WAN Software by sending crafted traffic. Successful exploitation could lead to arbitrary command execution with root privileges or denial of service through device reload. Affects Cisco IOS XE SD-WAN Software users.

📋 TL;DR

This vulnerability allows unauthenticated remote attackers to trigger a buffer overflow in Cisco IOS XE SD-WAN Software by sending crafted traffic. Successful exploitation could lead to arbitrary command execution with root privileges or denial of service through device reload. Affects Cisco IOS XE SD-WAN Software users.

💻 Affected Systems

Products:

Cisco IOS XE SD-WAN Software

Versions: Releases prior to 17.3.1a, 17.3.2, and 17.4.1

Operating Systems: Cisco IOS XE

Default Config Vulnerable: ⚠️ Yes

Notes: Affects devices running SD-WAN Software with vDaemon process enabled.

📦 What is this software?

Ios Xe Sd Wan by Cisco

View all CVEs affecting Ios Xe Sd Wan →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with root privileges leading to complete device compromise and potential network takeover.

🟠

Likely Case

Denial of service through device reload causing network disruption and service outages.

🟢

If Mitigated

Limited impact if proper network segmentation and access controls prevent unauthorized traffic.

🌐 Internet-Facing: HIGH - Unauthenticated remote exploitation makes internet-facing devices extremely vulnerable.

🏢 Internal Only: HIGH - Even internal devices are vulnerable to unauthenticated attacks from compromised internal hosts.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Unauthenticated remote exploitation with crafted traffic makes this relatively easy to exploit.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 17.3.1a, 17.3.2, 17.4.1 or later

Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxesdwan-rbuffover-vE2OB6tp

Restart Required: Yes

Instructions:

1. Download appropriate fixed software version from Cisco. 2. Backup current configuration. 3. Install update following Cisco IOS XE upgrade procedures. 4. Reboot device. 5. Verify successful upgrade.

🔧 Temporary Workarounds

Access Control List (ACL) Restriction

all

Implement ACLs to restrict access to vDaemon process ports from untrusted networks.

ip access-list extended BLOCK-VDAEMON
deny ip any any
interface GigabitEthernet0/0
ip access-group BLOCK-VDAEMON in

🧯 If You Can't Patch

Implement strict network segmentation to isolate affected devices from untrusted networks.
Deploy intrusion prevention systems (IPS) with signatures for this CVE to block exploitation attempts.

🔍 How to Verify

Check if Vulnerable:

Check IOS XE version with 'show version' command and compare to affected versions list.

Check Version:

show version | include Version

Verify Fix Applied:

Verify version is 17.3.1a, 17.3.2, 17.4.1 or later using 'show version' command.

📡 Detection & Monitoring

Log Indicators:

Device reload events without clear cause
vDaemon process crashes
Memory corruption warnings in system logs

Network Indicators:

Unusual traffic patterns to vDaemon ports
Crafted packets targeting SD-WAN devices

SIEM Query:

source="ios-xe" AND (event_type="crash" OR event_type="reload") AND process="vDaemon"

📊 Metadata

CVE ID: CVE-2021-34727

CVSS v3 Score: 9.8 (CRITICAL)

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

CWE: CWE-120

Published: September 23, 2021

Last Updated: November 21, 2024

🔗 References

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