CVE-2026-50186: 4gaBoards Path Traversal Vulnerability

CVE-2026-50186 Overview

CVE-2026-50186 is a path traversal vulnerability [CWE-22] in 4gaBoards, an open-source realtime project management board system. Versions prior to 3.3.8 fail to validate the filename parameter in GET /exports/:id/:filename. An authenticated project manager can inject traversal sequences such as ../ to read arbitrary files accessible to the server process. The same flaw triggers a subsequent fs.unlink() call against the attacker-controlled path, deleting the targeted file. The issue is fixed in version 3.3.8.

Critical Impact
Authenticated attackers can read and permanently delete arbitrary files readable by the 4gaBoards server process, resulting in data loss and denial of service.

Affected Products

4gaBoards versions prior to 3.3.8
server/api/controllers/boards/download.js (vulnerable controller)
server/api/helpers/boards/import-from-boards.js (related patched helper)

Discovery Timeline

2026-08-18 - CVE-2026-50186 published to NVD
2026-08-18 - Last updated in NVD database

Technical Details for CVE-2026-50186

Vulnerability Analysis

The vulnerability resides in the board export download handler at server/api/controllers/boards/download.js. The controller accepts a filename route parameter, URL-decodes it, and passes the value directly to path.join() beneath the private/exports/<user_id>/ directory. No containment or normalization check validates that the resolved path remains inside the intended export directory.

Because path.join() collapses ../ sequences during resolution, an attacker-supplied value can escape the export root and reference any file the Node.js process can access. The controller streams the resolved file back to the requester, exposing configuration files, credentials, or application source.

A second impact chains from the same flaw. When the file stream close handler fires, it passes the same attacker-controlled path to fs.unlink(), permanently removing the referenced file. This turns a read primitive into an arbitrary file deletion primitive with a single request.

Root Cause

The root cause is missing input sanitization on user-controlled filename input before filesystem operations. The controller trusts the decoded inputs.filename value and relies solely on path.join() for path construction, which does not enforce a directory boundary.

Attack Vector

An authenticated user with the project manager role sends a crafted GET /exports/:id/:filename request where :filename contains URL-encoded traversal sequences. The server resolves the traversed path, returns the file contents, then deletes the file after the stream closes.

javascript

// Patch excerpt from server/api/controllers/boards/download.js
+const { default: filenamify } = require('filenamify');
 const fs = require('fs');
-const path = require('path');
 
 const Errors = {
   BOARD_NOT_FOUND: {

Source: GitHub Commit 654151d

The fix replaces raw path composition with filenamify, which strips traversal characters and path separators from user-supplied filenames before filesystem access.

Detection Methods for CVE-2026-50186

Indicators of Compromise

HTTP requests to /exports/:id/:filename where the filename segment contains .., %2e%2e, %2f, or backslash sequences.
Unexpected access to sensitive files owned by the 4gaBoards process user, followed by their disappearance from disk.
Application errors referencing missing files under private/exports/ or outside the export root shortly after export requests.

Detection Strategies

Inspect web server and reverse proxy access logs for encoded traversal patterns in the filename path parameter of export routes.
Correlate authenticated export requests from project manager accounts with fs.unlink or file-deletion events at the OS layer.
Alert on 4gaBoards export responses returning file content types or sizes inconsistent with legitimate board export archives.

Monitoring Recommendations

Enable filesystem audit logging (auditd on Linux) on the 4gaBoards installation directory and any directory containing secrets accessible to the process user.
Baseline normal export request patterns per user and alert on high-frequency or anomalously targeted export downloads.
Track deletions of non-export files by the 4gaBoards service account as a high-fidelity indicator of exploitation.

How to Mitigate CVE-2026-50186

Immediate Actions Required

Upgrade 4gaBoards to version 3.3.8 or later, which introduces filenamify-based sanitization of the download filename parameter.
Audit accounts holding the project manager role and revoke any that are no longer required.
Review filesystem integrity and restore any files deleted through suspicious export requests from backup.

Patch Information

The fix is available in 4gaBoards Release v3.3.8. The patching commit is 654151d. Additional detail is available in the GitHub Security Advisory GHSA-rv7w-hhqv-65cf.

Workarounds

Restrict network access to the 4gaBoards instance to trusted users until the upgrade is applied.
Run the 4gaBoards process under a dedicated low-privilege service account with read access limited to its own data directory.
Deploy a reverse proxy or WAF rule that rejects requests to /exports/* containing .., %2e%2e, or encoded path separators in the filename segment.

bash

# Example nginx rule to block traversal attempts against the export endpoint
location ~ ^/exports/[^/]+/ {
    if ($request_uri ~* "(\.\.|%2e%2e|%2f|%5c)") {
        return 403;
    }
    proxy_pass http://4gaboards_upstream;
}