CVE-2025-3566: Echo Community System RCE Vulnerability

CVE-2025-3566 Overview

CVE-2025-3566 is an unrestricted file upload vulnerability in the veal98 Echo (小牛肉 Echo 开源社区系统) open source community system version 4.2. The flaw resides in the uploadMdPic function exposed through the /discuss/uploadMdPic endpoint. Attackers can manipulate the editormd-image-file argument to upload arbitrary files without restriction. The vulnerability is remotely exploitable and requires no authentication or user interaction. A proof-of-concept exploit has been publicly disclosed, increasing the risk of opportunistic attacks against exposed instances. The weakness is classified under [CWE-284] Improper Access Control.

Critical Impact
Unauthenticated remote attackers can upload arbitrary files to Echo 4.2 instances, potentially enabling webshell deployment and full application compromise.

Affected Products

veal98 Echo (小牛肉 Echo 开源社区系统) version 4.2
/discuss/uploadMdPic endpoint exposing the uploadMdPic function
Markdown editor image upload handler accepting the editormd-image-file parameter

Discovery Timeline

2025-04-14 - CVE-2025-3566 published to NVD
2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-3566

Vulnerability Analysis

The vulnerability resides in the uploadMdPic handler bound to the /discuss/uploadMdPic route in Echo 4.2. The handler accepts multipart file uploads through the editormd-image-file form parameter used by the Editor.md markdown component. Because the endpoint does not enforce file type, extension, or content validation, attackers can submit arbitrary file content under arbitrary filenames. The exploit has been published, making weaponization straightforward for unauthenticated network attackers.

Root Cause

The root cause is improper access control combined with missing input validation on the upload routine [CWE-284]. The uploadMdPic function trusts the client-supplied editormd-image-file parameter without verifying MIME type, magic bytes, file extension, or destination path. The endpoint also lacks authentication, so any remote client can invoke the upload. Together, these gaps allow uploads of executable server-side content such as JSP, JSPX, or other interpretable files.

Attack Vector

An attacker sends an HTTP POST request to /discuss/uploadMdPic with a multipart form body containing the editormd-image-file field. The attached payload can be a server-executable file rather than an image. After the file is written to a web-accessible directory, the attacker requests the resulting path to trigger execution. The attack requires no credentials, no privileges, and no user interaction, and can be launched directly across the network.

No verified exploit code is reproduced here. Refer to the published GitHub Proof of Concept and the VulDB entry #304607 for technical details.

Detection Methods for CVE-2025-3566

Indicators of Compromise

HTTP POST requests to /discuss/uploadMdPic containing the editormd-image-file multipart field with non-image content or executable extensions such as .jsp, .jspx, .war, or .php.
Newly created files in the Echo upload directory with server-executable extensions or mismatched MIME types versus magic bytes.
Outbound network connections originating from the Echo application process to unfamiliar hosts following an upload event.
Unusual GET requests retrieving recently uploaded files from the markdown image storage path.

Detection Strategies

Inspect web server and application logs for POST requests to /discuss/uploadMdPic from unauthenticated sessions or unknown source addresses.
Use a web application firewall (WAF) rule to flag uploads whose declared content type does not match the binary signature of the payload.
Correlate upload events with subsequent execution of new files inside the Echo deployment directory to identify webshell activity.

Monitoring Recommendations

Enable file integrity monitoring on the Echo upload and web root directories to capture file creation events in real time.
Forward Echo application, web server, and host process telemetry to a centralized analytics platform for correlation and retrospective hunting.
Alert on first-seen child processes spawned by the Echo Java or web server process, which often indicate webshell execution.

How to Mitigate CVE-2025-3566

Immediate Actions Required

Restrict network exposure of the /discuss/uploadMdPic endpoint until a fix is applied, ideally placing the application behind authenticated access controls or an allowlist.
Audit the Echo upload directory for unexpected files, particularly those with server-executable extensions, and remove any suspicious artifacts.
Deploy WAF rules that block uploads of non-image MIME types and reject file extensions outside an explicit allowlist (.jpg, .jpeg, .png, .gif, .webp).

Patch Information

No official vendor patch has been referenced in the available advisory data for CVE-2025-3566. Operators should monitor the upstream veal98 Echo project for updates and review the VulDB record #304607 for remediation status. Until a fix is published, apply the workarounds below.

Workarounds

Enforce authentication on the /discuss/uploadMdPic endpoint via a reverse proxy or application-layer middleware so that only authenticated community users can invoke the handler.
Configure the web server to disable script execution within the markdown image upload directory, for example by serving the directory as static content only.
Validate uploads server-side by checking magic bytes against an allowlist of image formats and rejecting any file whose extension or content does not match.
Rename uploaded files to randomized, server-generated identifiers without preserving the original client-supplied extension.

bash

# Example NGINX configuration disabling script execution in the upload path
location ^~ /upload/ {
    default_type application/octet-stream;
    types { }
    add_header Content-Disposition "attachment";
    location ~* \.(jsp|jspx|php|war|sh|py|pl)$ {
        deny all;
    }
}