CVE-2025-27134: Privilege Escalation Vulnerability in Joplin Note-Taking App

Overview

The CVE-2025-27134 vulnerability is a serious security flaw found in the Joplin note-taking application – one of today’s widely used open-source applications for managing notes and to-do lists. This vulnerability is particularly dangerous because it allows low-privileged users to perform administrative actions without proper authorization, thereby potentially compromising the system or leading to data leakage. This is a significant concern for both individuals and organizations as it could allow bad actors to gain unauthorized access to sensitive information or even take over systems.

Vulnerability Summary

CVE ID: CVE-2025-27134
Severity: High (8.8 CVSS Score)
Attack Vector: Network
Privileges Required: Low
User Interaction: None
Impact: System compromise and potential data leakage

Affected Products

Product | Affected Versions

Joplin | Prior to 3.3.3

How the Exploit Works

The exploit takes advantage of a flaw in Joplin’s server that allows non-admin users to access the `PATCH /api/users/:id` API endpoint and modify the `is_admin` field to 1. This implies that a low-privileged user can make themselves an admin without having the necessary permissions or the knowledge of the actual administrator. Once they grant themselves administrative privileges, they can perform actions typically reserved for admins, leading to potential system compromise or data leakage.

Conceptual Example Code

Below is a conceptual example of how the exploit might be carried out using an HTTP PATCH request.

PATCH /api/users/:id HTTP/1.1
Host: target.example.com
Content-Type: application/json
Authorization: Bearer {user_token}
{ "is_admin": 1 }

In this example, `:id` should be replaced with the user’s ID, and `{user_token}` should be replaced with the user’s token. Setting `is_admin` field to 1 grants the user administrative privileges.

Preventing the Exploit

The vulnerability has been patched in Joplin version 3.3.3. Users are strongly encouraged to update their Joplin installations to this version or later to mitigate the risk. If for some reason applying the vendor patch isn’t feasible immediately, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) could provide temporary protection by detecting and blocking attempts to exploit this vulnerability. However, this is a stopgap measure, and applying the patch is the most effective way to ensure security.