Code Signing Bypass on Windows in electron-updater < 6.3.0-alpha.6

Vulnerability Description

electron-updater allows for automatic updates for Electron apps. The file `packages/electron-updater/src/windowsExecutableCodeSignatureVerifier.ts` implements the signature validation routine for Electron applications on Windows. Because of the surrounding shell, a first pass by `cmd.exe` expands any environment variable found in command-line above. This creates a situation where `verifySignature()` can be tricked into validating the certificate of a different file than the one that was just downloaded. If the step is successful, the malicious update will be executed even if its signature is invalid. This attack assumes a compromised update manifest (server compromise, Man-in-the-Middle attack if fetched over HTTP, Cross-Site Scripting to point the application to a malicious updater server, etc.). The patch is available starting from 6.3.0-alpha.6.

References

• https://github.com/electron-userland/electron-builder/security/advisories/GHSA-9jxc-qjr9-vjxq
• https://github.com/electron-userland/electron-builder/pull/8295
• https://github.com/electron-userland/electron-builder/commit/ac2e6a25aa491c1ef5167a552c19fc2085cd427f
• https://github.com/electron-userland/electron-builder/blob/140e2f0eb0df79c2a46e35024e96d0563355fc89/packages/electron-updater/src/windowsExecutableCodeSignatureVerifier.ts#L35-L41