Session, Filen and Other Desktop Apps Still Trust the Cracked eMudhra Keys

What the Scan Found

Schärli, who spent this year publishing critiques of the encryption in Proton, Internxt and Filen, checked two things for each app. Does it still accept a certificate made with one of the cracked eMudhra keys? And does its updater verify the signature on a new version before installing it?

The answer depends on the system. On Linux, 11 of the 36 apps fail both checks, on Windows 9. On macOS none does, because the update framework Electron apps use there checks the developer’s code signature. Twenty apps on the Mac still trust the cracked keys, though.

He is open about how the list came together. An AI model compiled the apps, tested them in his lab and read their code to work out how each one updates. He warns that the table “may have misattributed something” and that he won’t keep it current as vendors patch.

The Electron versions are easy to check from the outside, and they hold up. For every app in the table below, the newest release in its public code repository matches his finding on whether it has the fix. Schärli also writes that he reported unchecked updates to Proton, Bitwarden, Internxt and Filen earlier this year.

How a Cracked Certificate Turns Into a Malware Risk

eMudhra is an Indian certificate authority, one of the companies whose certificates browsers and operating systems trust to vouch for websites. In October, a researcher known as Wayne found that eight of its intermediate certificates had private keys anyone could recover. According to BleepingComputer, the keys were generated in April 2025 with values below 256, so finding one took at most 255 guesses. With such a key, you can make a certificate for any website, and software that trusts eMudhra will believe it.

Firefox and Chrome blocked the certificates on 17 October, the day the flaw was reported. Microsoft followed on 20 October and Apple on 22 October. Browsers could move that fast because they receive blocklists in the background, without a new version.

Electron apps don’t get those lists. Electron packs Chromium into each app but leaves out the component that delivers them. The Electron team patched its supported versions on 22 October and was blunt about everything else: “There are no app side workarounds, you must update to a patched version of Electron.” Every vendor has to ship a new build, and every user has to install it.

That’s where the updater matters. An app that verifies the signature on an update installs only code its developer signed, even if someone tampers with the download. An app that doesn’t installs whatever the update server sends, or whoever is posing as that server. A fake certificate the app trusts is all it takes to pose convincingly.

Making one is no longer hard. The widely used interception tool mitmproxy added options on 22 October that sign certificates with the cracked keys. Schärli used them for his tests.

There’s no sign of attacks yet. Cloudflare wrote on 30 October that it had found “no evidence of the weak keys being used to intercept Cloudflare’s connections so far”, and added that this doesn’t rule out targeted interception.

Where Popular Privacy Apps Stand

These are the apps from the scan closest to privacy and security.

Session, Filen and Internxt are the clearest cases. All three ship an Electron version without the fix, and their newest releases switch off the Windows updater’s signature check in their build settings. Session and Internxt also run on Electron 40, which got no fixed build at all, so both need to move to a newer Electron line first. For an app like Session, built to keep even metadata away from prying eyes, that makes the computer it runs on the weak point. A fake update would run there like any program you install.

Bitwarden looks worse in the table than it is. Its updates are signed on Windows and macOS, and the Linux app doesn’t update itself. The fixed Electron (43.8.6) is already in its code repository, just not yet in a desktop release.

Proton Pass also runs an unpatched Electron, but it pins the certificates of Proton’s own servers, so its main traffic never trusts eMudhra, and the scan found no unchecked updates in it. Proton Mail’s desktop app has the fix. On Windows, its updates still go unchecked through a separate installer called Squirrel, which relies on the Windows list of trusted certificates. Microsoft blocked the cracked ones there on 20 October.

Signal shows the other end. It has had the fix since version 8.32.0, and on Windows its updates carry Signal’s own signature, checked before anything is installed.

What to Do if You Use One of These Apps

• Update from your browser, not the app. When a fixed version comes out, download it from the developer’s website. Your browser already rejects the cracked certificates, so the download can’t be swapped the same way. This matters most for the apps whose updater skips the signature check.
• Pause automatic updates in those apps if they let you, until the fixed release is out, and check the developer’s site for it.
• Mind the network. The attack needs someone between you and the app’s servers, such as whoever runs a hotel or café network, or anyone who has taken over the router. On your own home network, the risk is much smaller.
• A VPN helps on public Wi-Fi, but it’s not the fix. It keeps others on the same hotspot out of your traffic. The app still trusts the cracked keys, and the path from the VPN server onward isn’t covered.
• Keep your system updated, especially on Windows, where apps that update through Squirrel rely on Windows’ own certificate list.

Schärli’s own advice goes further. He tells users to uninstall the affected apps until fixed versions exist. If you use one of them on Windows or Linux and often work on networks you don’t control, that’s the safer choice. Filen, Internxt, Notesnook and Standard Notes also run in the browser, which already rejects the cracked certificates.