Comprehensive Technical Analysis of CVE-2023-33236

CVE ID: CVE-2023-33236 Vendor: Moxa Product: MXsecurity (Version 1.0) Vulnerability Type: Hardcoded Credentials Leading to Authentication Bypass via JWT Token Forgery CVSS v3.1 Score: 9.8 (Critical) – AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Published: May 22, 2023 Source: Moxa PSIRT

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1. Vulnerability Assessment and Severity Evaluation

Vulnerability Overview

CVE-2023-33236 is a hardcoded credential vulnerability in Moxa’s MXsecurity version 1.0, which allows attackers to craft arbitrary JSON Web Tokens (JWTs) and bypass authentication for web-based APIs. The flaw stems from the use of static, embedded credentials within the application, which can be extracted and exploited to generate valid authentication tokens without legitimate user credentials.

Severity Justification (CVSS 9.8 - Critical)

The CVSS v3.1 score of 9.8 (Critical) is justified by the following metrics:

Metric	Value	Explanation
Attack Vector (AV)	Network (N)	Exploitable remotely over the network without physical access.
Attack Complexity (AC)	Low (L)	No specialized conditions required; exploitation is straightforward.
Privileges Required (PR)	None (N)	No prior authentication or privileges needed.
User Interaction (UI)	None (N)	No user interaction is required.
Scope (S)	Unchanged (U)	The vulnerability affects the vulnerable component (MXsecurity) only.
Confidentiality (C)	High (H)	Attackers can access sensitive data via API endpoints.
Integrity (I)	High (H)	Attackers can modify or inject data via forged JWTs.
Availability (A)	High (H)	Potential for denial-of-service (DoS) or unauthorized control.

Risk Assessment

• Exploitability: High – The vulnerability is trivially exploitable with minimal technical knowledge.
• Impact: Severe – Full authentication bypass enables unauthorized access, data exfiltration, and potential lateral movement within the network.
• Likelihood of Exploitation: High – Hardcoded credentials are a well-known attack vector, and JWT forgery is a common exploitation technique.

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2. Potential Attack Vectors and Exploitation Methods

Attack Vectors

1. Remote Exploitation via API Abuse

   • Attackers can intercept or reverse-engineer the MXsecurity application to extract hardcoded JWT signing keys.
   • Once obtained, they can forge arbitrary JWTs with elevated privileges (e.g., admin access).

2. Man-in-the-Middle (MitM) Attacks

   • If the application uses unencrypted HTTP (or weak HTTPS configurations), attackers can intercept JWTs and modify them.
   • Even if HTTPS is enforced, hardcoded keys allow offline JWT forgery.

3. Supply Chain Attacks

   • If the hardcoded credentials are shared across multiple Moxa products, exploitation could extend beyond MXsecurity.

Exploitation Steps

1. Reconnaissance

   • Identify the MXsecurity API endpoints (e.g., /api/auth, /api/users).
   • Use tools like Burp Suite, Postman, or OWASP ZAP to analyze API requests.

2. Extract Hardcoded Credentials

   • Reverse-engineer the MXsecurity binary (e.g., using Ghidra, IDA Pro, or Binary Ninja) to locate hardcoded JWT signing keys.
   • Alternatively, brute-force weak JWT secrets using tools like jwt_tool or John the Ripper.

3. JWT Forgery

   • Craft a malicious JWT with:
     • A valid signature (using the extracted key).
     • Arbitrary claims (e.g., admin: true, exp: 9999999999).
   • Example (using jwt_tool):

     jwt_tool.py -S hs256 -p "extracted_hardcoded_key" -I -pc "admin" -pv "true" "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkFkbWluIiwiaWF0IjoxNTE2MjM5MDIyfQ"
     

4. Authentication Bypass

   • Submit the forged JWT to the API endpoint (e.g., /api/admin/dashboard).
   • Gain unauthorized access to sensitive functions (e.g., user management, system configuration).

5. Post-Exploitation

   • Data Exfiltration: Extract sensitive information (e.g., user credentials, network configurations).
   • Privilege Escalation: Modify user roles or create new admin accounts.
   • Lateral Movement: Use compromised credentials to access other systems in the network.

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3. Affected Systems and Software Versions

Vulnerable Product

• Moxa MXsecurity Version 1.0

Potential Impact on Other Systems

• If the hardcoded credentials are reused in other Moxa products (e.g., industrial switches, gateways), those systems may also be at risk.
• Third-party integrations using MXsecurity APIs may inherit the vulnerability.

Verification Steps

• Check installed version:

  curl -X GET "http://<MXsecurity_IP>/api/version" -H "Authorization: Bearer <JWT>"
  

• Test for hardcoded JWT keys:
  • Use jwt_tool to attempt brute-forcing:

    jwt_tool.py -t "http://<MXsecurity_IP>/api/auth" -rc "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..." -M at
    

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4. Recommended Mitigation Strategies

Immediate Actions (Short-Term)

1. Apply Vendor Patches

   • Moxa has released a security advisory with patches. Upgrade to the latest secure version immediately.
   • Reference: Moxa Security Advisory

2. Temporary Workarounds

   • Network Segmentation: Isolate MXsecurity from untrusted networks (e.g., internet, guest Wi-Fi).
   • Firewall Rules: Restrict API access to whitelisted IPs only.
   • Disable Unused APIs: If certain endpoints are not required, disable them via configuration.

3. JWT Hardening

   • Rotate JWT Signing Keys: Replace hardcoded keys with dynamically generated, short-lived keys.
   • Enforce Strong Algorithms: Use HS512 or RS512 instead of HS256.
   • Implement JWT Expiry: Set short-lived tokens (e.g., 5-15 minutes) with refresh tokens.

Long-Term Remediation (Strategic)

1. Secure Development Practices

   • Eliminate Hardcoded Credentials: Use environment variables or secure vaults (e.g., HashiCorp Vault, AWS Secrets Manager).
   • Static & Dynamic Analysis: Integrate SAST/DAST tools (e.g., SonarQube, Burp Suite) into CI/CD pipelines.
   • Code Reviews: Enforce peer reviews for authentication-related code.

2. Enhanced Authentication Mechanisms

   • Multi-Factor Authentication (MFA): Enforce MFA for API access.
   • OAuth 2.0 / OpenID Connect: Replace JWT-based auth with standardized protocols.
   • Rate Limiting: Implement API throttling to prevent brute-force attacks.

3. Monitoring & Detection

   • SIEM Integration: Monitor for unusual JWT usage (e.g., multiple failed auth attempts, tokens with excessive privileges).
   • Anomaly Detection: Use UEBA (User and Entity Behavior Analytics) to detect JWT forgery attempts.
   • Logging: Ensure detailed audit logs for all authentication events.

4. Incident Response Planning

   • Develop a Playbook: Define steps for JWT compromise response (e.g., key rotation, user revocation).
   • Regular Penetration Testing: Conduct red team exercises to test authentication bypass resilience.

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5. Impact on the Cybersecurity Landscape

Broader Implications

1. Industrial Control Systems (ICS) Risk

   • MXsecurity is used in OT (Operational Technology) environments, where authentication bypass can lead to physical system manipulation (e.g., disabling security cameras, altering access controls).
   • Potential for cascading failures in critical infrastructure (e.g., power grids, manufacturing).

2. Supply Chain & Third-Party Risk

   • If Moxa’s hardcoded credentials are reused in other products, the vulnerability could propagate across vendors.
   • Third-party integrations (e.g., SIEM, SCADA) may inherit the risk.

3. Regulatory & Compliance Impact

   • NIST SP 800-53 (AC-14, IA-5): Non-compliance due to hardcoded credentials.
   • ISO 27001 (A.9.4.2, A.14.2.1): Failure to implement secure authentication.
   • GDPR (Article 32): Risk of unauthorized data access leading to regulatory fines.

4. Exploitation Trends

   • Increased Targeting of ICS/OT: Attackers are actively exploiting hardcoded credentials in industrial devices (e.g., CVE-2021-22893, CVE-2020-14511).
   • JWT Abuse in the Wild: Forged JWTs are a growing attack vector (e.g., CVE-2022-21449, CVE-2021-41773).

Historical Context

• Similar Vulnerabilities:
  • CVE-2021-44228 (Log4Shell): Hardcoded credentials in logging libraries.
  • CVE-2020-1938 (Ghostcat): Hardcoded credentials in Apache Tomcat.
  • CVE-2019-1653 (Cisco RV320): Hardcoded credentials in router firmware.

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6. Technical Details for Security Professionals

Root Cause Analysis

• Hardcoded JWT Signing Key:

  • The MXsecurity application embeds a static HMAC-SHA256 key within its binary.
  • This key is used to sign and verify JWTs, allowing attackers to replicate the signing process.

• Weak JWT Implementation:

  • No key rotation (static key remains unchanged).
  • No algorithm enforcement (allows weak algorithms like none or HS256).
  • No token expiration checks (long-lived or infinite tokens).

Exploitation Proof of Concept (PoC)

1. Extract the Hardcoded Key

   • Method 1: Binary Analysis

     • Use Ghidra to decompile the MXsecurity binary.
     • Search for JWT-related strings (e.g., "secret", "HS256", "sign").
     • Locate the hardcoded key (e.g., "MoxaSecret123!").

   • Method 2: Brute-Force Attack

     • Use jwt_tool to brute-force the key:

       jwt_tool.py -t "http://<MXsecurity_IP>/api/auth" -rc "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..." -M at -d /path/to/wordlist.txt
       

2. Forge a Malicious JWT

   • Example Payload (Admin Access):

     {
       "sub": "admin",
       "role": "administrator",
       "iat": 1684742400,
       "exp": 1900000000
     }
     

   • Sign with Extracted Key:

     jwt_tool.py -S hs256 -p "MoxaSecret123!" -I -pc "role" -pv "administrator" "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJhZG1pbiIsInJvbGUiOiJ1c2VyIiwiaWF0IjoxNjg0NzQyNDAwfQ"
     

3. Bypass Authentication

   • Send the Forged JWT to an Admin Endpoint:

     curl -X GET "http://<MXsecurity_IP>/api/admin/users" -H "Authorization: Bearer <FORGED_JWT>"
     

Detection & Forensics

1. Indicators of Compromise (IoCs)

   • Unusual JWT Claims: Tokens with admin: true, exp: 9999999999.
   • Multiple Failed Auth Attempts: Brute-force attempts in logs.
   • Anomalous API Calls: Requests to /api/admin from unexpected IPs.

2. Log Analysis

   • Check for:
     • JWTs with identical signatures (indicating hardcoded key usage).
     • Unexpected admin logins (e.g., user: "admin" from unknown sources).
   • Example Log Entry:

     [2023-05-25 14:30:45] INFO: Successful API access - User: "admin", JWT: "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...", IP: 192.168.1.100
     

3. Memory Forensics

   • Volatility / Rekall: Check for hardcoded keys in memory.
   • Example Command:

     volatility -f mxsecurity_memory.dmp --profile=LinuxMXsecurityx64 linux_bash
     

Defensive Techniques

1. JWT Security Best Practices

   • Use Asymmetric Signing (RS256/ES256): Prevents key extraction from client-side.
   • Short-Lived Tokens: Enforce 5-15 minute expiry.
   • Token Revocation: Implement a blacklist for compromised tokens.

2. Runtime Application Self-Protection (RASP)

   • JWT Validation Hooks: Detect and block malformed or forged tokens.
   • Behavioral Analysis: Flag unusual token usage patterns.

3. Network-Level Protections

   • WAF Rules: Block JWT manipulation attempts (e.g., alg: none attacks).
   • Zero Trust Architecture: Enforce continuous authentication.

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Conclusion & Recommendations

CVE-2023-33236 represents a critical authentication bypass vulnerability due to hardcoded JWT signing keys in Moxa MXsecurity. The flaw is easily exploitable and poses severe risks to industrial and enterprise environments.

Key Takeaways for Security Teams

✅ Patch Immediately: Apply Moxa’s security updates without delay. ✅ Harden JWT Implementations: Rotate keys, enforce strong algorithms, and implement short-lived tokens. ✅ Monitor for Exploitation: Deploy SIEM rules to detect JWT forgery attempts. ✅ Conduct a Security Audit: Review all hardcoded credentials in deployed systems. ✅ Educate Developers: Train teams on secure authentication practices.

Final Risk Rating

Factor	Rating
Exploitability	High
Impact	Critical
Likelihood	High
Overall Risk	Critical

Action Priority: Urgent – Immediate patching and mitigation required to prevent unauthorized access and potential data breaches.

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References:

• Moxa Security Advisory
• NIST NVD Entry for CVE-2023-33236
• OWASP JWT Cheat Sheet