CVE-2021-3849 – An authentication bypass vulnerability in Lenov... (How to Fix)

Q: What is the severity of CVE-2021-3849?

CVE-2021-3849 has a CVSS score of 9.8 (CRITICAL). An authentication bypass vulnerability in Lenovo Fan Power Controller2 (FPC2) and System Management Module (SMM) firmware allows unauthenticated attackers to execute arbitrary commands on affected devices. This affects organizations using these Lenovo hardware management components. SMM2 is not vulnerable.

📋 TL;DR

An authentication bypass vulnerability in Lenovo Fan Power Controller2 (FPC2) and System Management Module (SMM) firmware allows unauthenticated attackers to execute arbitrary commands on affected devices. This affects organizations using these Lenovo hardware management components. SMM2 is not vulnerable.

💻 Affected Systems

Products:

Lenovo Fan Power Controller2 (FPC2)
Lenovo System Management Module (SMM)

Versions: Specific vulnerable versions not publicly detailed in advisory

Operating Systems: Embedded firmware

Default Config Vulnerable: ⚠️ Yes

Notes: SMM2 is not affected. Requires web interface access to vulnerable components.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete compromise of hardware management systems allowing attackers to execute arbitrary commands, potentially leading to data center disruption, hardware damage, or lateral movement into connected systems.

🟠

Likely Case

Unauthenticated attackers gaining administrative control over hardware management interfaces, enabling system manipulation, data exfiltration, or service disruption.

🟢

If Mitigated

Limited impact if systems are isolated, patched, or have additional authentication layers preventing network access to vulnerable interfaces.

🌐 Internet-Facing: HIGH - Web interfaces exposed to internet could be directly exploited by any remote attacker without authentication.

🏢 Internal Only: HIGH - Even internally, unauthenticated attackers on the network can exploit this vulnerability to gain administrative control.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Authentication bypass vulnerabilities typically have low exploitation complexity once the bypass method is understood.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Not specified in advisory - refer to Lenovo security updates

Vendor Advisory: https://support.lenovo.com/us/en/product_security/LEN-72615

Restart Required: Yes

Instructions:

1. Access Lenovo support portal 2. Download latest firmware for FPC2/SMM 3. Apply firmware update following Lenovo documentation 4. Reboot affected devices 5. Verify update successful

🔧 Temporary Workarounds

Network Isolation

all

Restrict network access to FPC2/SMM web interfaces using firewall rules or network segmentation

Access Control

all

Implement additional authentication layers or restrict access to trusted IP addresses only

🧯 If You Can't Patch

Isolate affected systems on separate VLAN with strict access controls
Monitor network traffic to/from FPC2/SMM interfaces for suspicious activity

🔍 How to Verify

Check if Vulnerable:

Check firmware version against Lenovo security advisory LEN-72615 and verify if web interface allows unauthenticated command execution

Check Version:

Check via web interface or Lenovo management tools - specific command varies by implementation

Verify Fix Applied:

Verify firmware has been updated to latest version and test authentication requirements for web interface access

📡 Detection & Monitoring

Log Indicators:

Unauthenticated access to web interface
Unexpected command execution events
Authentication bypass attempts

Network Indicators:

Unusual traffic to FPC2/SMM web ports (typically 80/443)
Unauthenticated API calls to management interfaces

SIEM Query:

source_ip=* AND (dest_port=80 OR dest_port=443) AND dest_ip=FPC2/SMM_IP AND http_status=200 AND auth_failure=false

📊 Metadata

CVE ID: CVE-2021-3849

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-288

Published: April 22, 2022

Last Updated: November 21, 2024

🔗 References

https://support.lenovo.com/us/en/product_security/LEN-72615 Vendor Advisory
https://support.lenovo.com/us/en/product_security/LEN-72615 Vendor Advisory

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