CVE-2026-70603: Electron Path Traversal Vulnerability

CVE-2026-70603 Overview

CVE-2026-70603 is an input validation vulnerability in Electron, the framework for building cross-platform desktop applications with JavaScript, HTML, and CSS. The shell.openPath() API does not reject file paths containing embedded null bytes. Applications that perform string-only validation, such as checking a file extension before passing the path to shell.openPath(), can be bypassed. An attacker who controls the input path can cause the application to open a different file than the one that passed validation. The issue is fixed in Electron versions 39.8.6, 40.9.0, 41.1.1, and 42.0.0-beta.1.

Critical Impact
Attackers can bypass file-extension or string-based path validation in Electron apps, causing shell.openPath() to open an unintended file supplied through untrusted input.

Affected Products

Electron versions prior to 39.8.6
Electron 40.x prior to 40.9.0 and 41.x prior to 41.1.1
Electron 42.x prior to 42.0.0-beta.1

Discovery Timeline

2026-08-05 - CVE-2026-70603 published to NVD
2026-08-06 - Last updated in NVD database

Technical Details for CVE-2026-70603

Vulnerability Analysis

The vulnerability is an improper input validation flaw [CWE-20] in Electron's shell.openPath() function. The API accepts strings containing embedded null bytes (\0) without rejecting them. Many operating system APIs treat the null byte as a string terminator, so a path like document.pdf\0.exe may pass an application-level extension check while resolving to a different file at the filesystem layer.

Exploitation requires local access, user interaction, and existing low privileges. An application is only affected when it derives paths from untrusted input and relies exclusively on string comparisons rather than filesystem-level checks.

Root Cause

The root cause is missing sanitization of embedded null bytes in the path argument passed to shell.openPath(). Application developers commonly validate paths by inspecting the extension suffix or matching against an allowlist. Because the null byte is not rejected by Electron and is interpreted as a string terminator by native OS handlers, the validated string and the actually opened file diverge. The patched releases add null-byte rejection inside shell.openPath().

Attack Vector

An attacker supplies a crafted path such as safe.txt\0malicious.html through an application input channel, for example a file picker filter, an IPC message, or a URI handler. The Electron app validates the trailing extension (.html) or the visible prefix (safe.txt) and passes the path to shell.openPath(). The underlying shell handler truncates at the null byte or otherwise resolves a different target, causing the wrong file to be opened. See the GitHub Security Advisory GHSA-5c9j-mhmv-5xgx for the maintainer's technical description.

Detection Methods for CVE-2026-70603

Indicators of Compromise

File paths or IPC messages containing embedded null bytes (\\x00) delivered to Electron-based desktop applications.
shell.openPath() invocations where the resolved file differs from the string logged by the application.
Unexpected process launches spawned by an Electron parent process shortly after a file-open action initiated from untrusted input.

Detection Strategies

Audit source code for calls to shell.openPath() that consume paths from untrusted sources without a filesystem existence or canonicalization check.
Instrument application logging to record the raw byte sequence of file paths, not the display string, so null bytes are visible during review.
Correlate Electron process telemetry with child-process creation events to identify anomalous file handlers being invoked after user file-open actions.

Monitoring Recommendations

Monitor endpoint telemetry for Electron applications spawning executables or scripts from paths that contain non-printable characters.
Track application updates and flag deployed Electron builds still running versions prior to 39.8.6, 40.9.0, or 41.1.1.
Alert on IPC payloads or command-line arguments containing %00 or raw \0 bytes reaching Electron main-process code paths.

How to Mitigate CVE-2026-70603

Immediate Actions Required

Upgrade Electron to 39.8.6, 40.9.0, 41.1.1, or 42.0.0-beta.1 and rebuild affected desktop applications.
Inventory internally developed and third-party Electron apps to determine exposure to vulnerable versions.
Review application code for any call to shell.openPath() that receives user-controlled input and add explicit null-byte rejection.

Patch Information

Electron maintainers fixed the issue in versions 39.8.6, 40.9.0, 41.1.1, and 42.0.0-beta.1 by rejecting paths that contain embedded null bytes inside shell.openPath(). Details are published in the Electron GitHub Security Advisory GHSA-5c9j-mhmv-5xgx.

Workarounds

Reject any file path containing a null byte (\\x00) before passing it to shell.openPath().
Replace string-only validation with filesystem-based checks such as fs.stat() or path.resolve() followed by extension inspection of the resolved path.
Restrict shell.openPath() usage to paths generated by the application itself rather than paths derived from user or network input.

bash

# Node.js validation example for Electron main process
if (userPath.includes('\0')) {
  throw new Error('Invalid path: embedded null byte');
}