CVE-2021-1572 – CVE-2021-1572 is a privilege escalation vulnera... (How to Fix)

Q: What is the severity of CVE-2021-1572?

CVE-2021-1572 has a CVSS score of 7.8 (HIGH). CVE-2021-1572 is a privilege escalation vulnerability in Cisco ConfD software that allows authenticated local attackers to execute arbitrary commands as root. The vulnerability occurs when the ConfD built-in SSH server is enabled, causing the SFTP user service to run with elevated privileges. Any user with valid credentials on an affected device can exploit this to gain root access.

📋 TL;DR

CVE-2021-1572 is a privilege escalation vulnerability in Cisco ConfD software that allows authenticated local attackers to execute arbitrary commands as root. The vulnerability occurs when the ConfD built-in SSH server is enabled, causing the SFTP user service to run with elevated privileges. Any user with valid credentials on an affected device can exploit this to gain root access.

💻 Affected Systems

Products:

Cisco ConfD
Cisco Network Services Orchestrator (NSO)

Versions: ConfD 6.x and 7.x versions prior to 7.4.1, NSO versions with vulnerable ConfD components

Operating Systems: Linux-based systems running ConfD

Default Config Vulnerable: ⚠️ Yes

Notes: Only vulnerable if ConfD built-in SSH server is enabled. If SSH server is disabled, system is not affected.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Attacker gains full root access to the system, enabling complete compromise, data theft, persistence, and lateral movement.

🟠

Likely Case

Privileged user or compromised account escalates to root to install malware, steal sensitive data, or pivot to other systems.

🟢

If Mitigated

Attack is prevented through patching or disabling the vulnerable SSH server, limiting impact to normal user privileges.

🌐 Internet-Facing: MEDIUM - Requires SSH access to be internet-facing and attacker needs valid credentials.

🏢 Internal Only: HIGH - Internal attackers with any valid credentials can exploit this to gain root access on affected systems.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: LOW

Exploitation requires valid user credentials and access to the SFTP interface. Attack chain is straightforward once authenticated.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: ConfD 7.4.1 and later, NSO versions with updated ConfD components

Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-confd-priv-esc-LsGtCRx4

Restart Required: Yes

Instructions:

1. Download and install ConfD 7.4.1 or later from Cisco. 2. Apply the patch to all affected systems. 3. Restart ConfD services. 4. Verify the SSH server configuration is properly secured.

🔧 Temporary Workarounds

Disable ConfD Built-in SSH Server

linux

Disable the vulnerable SSH server component to prevent exploitation

confd --stop-ssh
Edit ConfD configuration to disable SSH server

Restrict SSH Access

all

Limit SSH access to trusted users and networks only

Configure firewall rules to restrict SSH port access
Use SSH key authentication only

🧯 If You Can't Patch

Disable the ConfD built-in SSH server immediately
Implement strict access controls and monitor all SSH authentication attempts

🔍 How to Verify

Check if Vulnerable:

Check ConfD version with 'confd --version' and verify if SSH server is enabled in configuration

Check Version:

confd --version

Verify Fix Applied:

Verify ConfD version is 7.4.1 or later and test privilege escalation attempts fail

📡 Detection & Monitoring

Log Indicators:

Unusual SFTP command sequences
Multiple failed then successful SSH logins
Privilege escalation attempts in system logs

Network Indicators:

Unusual SSH traffic patterns to ConfD systems
SFTP connections followed by privileged commands

SIEM Query:

source="confd.log" AND ("SFTP" OR "privilege") AND ("escalation" OR "root")

📊 Metadata

CVE ID: CVE-2021-1572

CVSS v3 Score: 7.8 (HIGH)

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

CWE: CWE-266

Published: August 4, 2021

Last Updated: November 21, 2024

🔗 References

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