Comprehensive Technical Analysis of CVE-2021-28411

CVE ID: CVE-2021-28411 CVSS Score: 9.8 (Critical) Affected Software: RuoYi v3.4.0 (Java-based enterprise management framework) Vulnerability Type: Insecure Deserialization Leading to Privilege Escalation

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1. Vulnerability Assessment & Severity Evaluation

Vulnerability Overview

CVE-2021-28411 is an insecure deserialization vulnerability in the CookieRememberMeManager class of RuoYi v3.4.0, specifically within the getRememberedSerializedIdentity function. The flaw allows remote attackers to execute arbitrary code or escalate privileges by manipulating the "remember me" cookie, which is deserialized without proper validation.

CVSS v3.1 Breakdown (Score: 9.8 - Critical)

Metric	Value	Explanation
Attack Vector (AV)	Network (N)	Exploitable remotely over HTTP/HTTPS.
Attack Complexity (AC)	Low (L)	No special conditions required; trivial to exploit.
Privileges Required (PR)	None (N)	No authentication needed.
User Interaction (UI)	None (N)	No user interaction required.
Scope (S)	Changed (C)	Impact extends beyond the vulnerable component (privilege escalation).
Confidentiality (C)	High (H)	Full system compromise possible.
Integrity (I)	High (H)	Arbitrary code execution enables data tampering.
Availability (A)	High (H)	Denial-of-service or full system takeover possible.

Severity Justification

• Critical Impact: Successful exploitation can lead to remote code execution (RCE), privilege escalation to admin, or complete system compromise.
• Low Barrier to Exploitation: No authentication or user interaction is required, making it highly attractive to attackers.
• Widespread Deployment: RuoYi is widely used in enterprise environments, increasing the potential attack surface.

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2. Potential Attack Vectors & Exploitation Methods

Attack Vector: Insecure Deserialization of "Remember Me" Cookie

The vulnerability stems from improper handling of serialized Java objects in the CookieRememberMeManager class. The getRememberedSerializedIdentity function deserializes user-controlled cookie data without:

• Input validation (e.g., checking for malicious payloads).
• Signature verification (e.g., HMAC to ensure integrity).
• Safe deserialization practices (e.g., using ObjectInputStream with a whitelist).

Exploitation Steps

1. Craft a Malicious "Remember Me" Cookie

   • An attacker generates a malicious serialized Java object (e.g., using ysoserial or custom payloads).
   • Common gadget chains (e.g., CommonsCollections, Groovy, Spring) can be embedded to achieve RCE.

2. Send the Malicious Cookie to the Target

   • The attacker sends an HTTP request with the crafted cookie to the vulnerable RuoYi instance.
   • Example:

     GET /dashboard HTTP/1.1
     Host: vulnerable-ruoyi.example.com
     Cookie: rememberMe=malicious_serialized_payload
     

3. Deserialization & Code Execution

   • The server deserializes the cookie, triggering the malicious payload.
   • Depending on the gadget chain, the attacker may:
     • Execute arbitrary commands (e.g., reverse shell, file upload).
     • Escalate privileges (e.g., gain admin access).
     • Exfiltrate sensitive data (e.g., database credentials).

Proof-of-Concept (PoC) Considerations

• Tools: ysoserial, Burp Suite, Java deserialization payload generators.
• Gadget Chains: Commonly exploited chains include:
  • CommonsCollections1 (RCE via InvokerTransformer).
  • Groovy1 (RCE via MethodClosure).
  • Spring1 (RCE via MethodInvokingFactoryBean).

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3. Affected Systems & Software Versions

Software	Affected Versions	Fixed Versions	Notes
RuoYi	v3.4.0	v3.4.1+ (or later)	Only v3.4.0 is confirmed vulnerable.
Dependencies	Apache Shiro (if used)	N/A	Some RuoYi deployments may use Shiro for auth.

Detection Methods

• Manual Inspection:
  • Check for CookieRememberMeManager in shiro.ini or Spring configuration.
  • Verify if getRememberedSerializedIdentity lacks proper validation.
• Automated Scanning:
  • Nessus, OpenVAS, Burp Suite (with deserialization checks).
  • Custom scripts to detect vulnerable cookie handling.

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4. Recommended Mitigation Strategies

Immediate Remediation (Short-Term)

1. Disable "Remember Me" Functionality

   • Remove or disable the CookieRememberMeManager in shiro.ini:

     # securityManager.rememberMeManager = $rememberMeManager
     

   • Alternatively, set rememberMe.cookie.maxAge = 0.

2. Upgrade RuoYi

   • Apply the latest patch (v3.4.1 or later) from the official repository.

3. Implement Input Validation

   • Use HMAC signing for serialized cookies to ensure integrity.
   • Example (Java):

     byte[] serialized = Base64.decode(cookieValue);
     if (!verifyHmac(serialized, secretKey)) {
         throw new SecurityException("Invalid cookie signature");
     }
     

Long-Term Security Hardening

1. Use Safe Deserialization Libraries

   • Replace ObjectInputStream with safe alternatives:
     • Jackson (with JsonDeserializer).
     • Gson (for JSON-based serialization).
     • Apache Commons Lang (with SerializationUtils and whitelisting).

2. Enable Java Security Manager

   • Restrict deserialization to trusted classes:

     System.setProperty("java.security.policy", "deserialization.policy");
     

3. Network-Level Protections

   • Web Application Firewall (WAF) rules to block malicious cookie patterns.
   • Rate limiting to prevent brute-force attacks.

4. Monitoring & Logging

   • Log all deserialization attempts (successful/failed).
   • Alert on suspicious cookie values (e.g., long Base64 strings).

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5. Impact on the Cybersecurity Landscape

Enterprise Risk

• High-Value Target: RuoYi is widely used in Chinese enterprise environments, making it a prime target for APT groups and cybercriminals.
• Supply Chain Risks: Vulnerable RuoYi instances may be embedded in third-party applications, increasing exposure.

Exploitation Trends

• Active Exploitation: Similar deserialization flaws (e.g., CVE-2016-4437 in Apache Shiro) have been exploited in the wild.
• Ransomware & Data Theft: Attackers may use this to deploy ransomware or exfiltrate sensitive data.

Regulatory & Compliance Implications

• GDPR, CCPA, NIST: Unpatched vulnerabilities may lead to data breaches, resulting in fines and legal consequences.
• CISA KEV Catalog: This CVE may be added to the Known Exploited Vulnerabilities list, requiring federal agencies to patch within deadlines.

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6. Technical Details for Security Professionals

Root Cause Analysis

The vulnerability exists in the CookieRememberMeManager class, where the getRememberedSerializedIdentity method:

1. Decodes a Base64-encoded cookie (rememberMe).
2. Deserializes the raw bytes using ObjectInputStream without validation.
3. Returns the deserialized object as a PrincipalCollection, which may contain malicious payloads.

Vulnerable Code Snippet (Pseudocode):

public PrincipalCollection getRememberedSerializedIdentity(SubjectContext subjectContext) {
    String base64 = WebUtils.getCookie(subjectContext, "rememberMe");
    byte[] serialized = Base64.decode(base64);
    ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(serialized));
    return (PrincipalCollection) ois.readObject(); // UNSAFE DESERIALIZATION
}

Exploitation Gadget Chains

Attackers can leverage Java deserialization gadgets to achieve RCE. Common chains include:

Gadget Chain	Impact	Tools
CommonsCollections1	RCE via InvokerTransformer	ysoserial
Groovy1	RCE via MethodClosure	ysoserial
Spring1	RCE via MethodInvokingFactoryBean	Custom payloads

Forensic & Incident Response Considerations

1. Indicators of Compromise (IoCs):

   • Unusual rememberMe cookie values (long Base64 strings).
   • Suspicious process execution (e.g., curl, bash, powershell).
   • Unexpected network connections (e.g., reverse shells).

2. Memory Forensics:

   • Use Volatility or Rekall to detect injected payloads.
   • Check for unusual Java threads (e.g., ProcessBuilder execution).

3. Log Analysis:

   • Review HTTP access logs for rememberMe cookie anomalies.
   • Check application logs for deserialization errors.

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Conclusion & Recommendations

CVE-2021-28411 is a critical deserialization vulnerability with severe implications for affected RuoYi deployments. Organizations must:

1. Patch immediately (upgrade to v3.4.1+).
2. Disable "Remember Me" if patching is not feasible.
3. Implement safe deserialization practices (HMAC, whitelisting).
4. Monitor for exploitation attempts (WAF, logging).

Given the high CVSS score (9.8) and active exploitation risks, this vulnerability should be treated as a top priority in vulnerability management programs.

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References:

• RuoYi GitHub Issue #20
• OWASP Deserialization Cheat Sheet
• CISA Known Exploited Vulnerabilities Catalog