When you visit a secure website, your browser trusts a 'certificate' to prove the site is real. A company called eMudhra made weak secret keys for 8 of its certificate makers. Someone could use them to make fake certificates and pretend to be any website. Mozilla, Google, Apple and Microsoft all blocked those keys in the days after Oct 17. Most of this is automatic. Make sure your browser and your computer are up to date.
- Status
- Partly patched
- Being attacked?
- No[2]
- Severity
- High
- Updated
Google says no fake certificates were found in public records before it blocked the keys. The company (eMudhra) says it issued no certificates from those keys. Severity: Mozilla and Google both treat it as a serious break in website trust. No score exists. First reported .
Am I affected?
Most people are already protected because the block went out by itself within hours. Browsers and computers that were offline, or had special settings, may be behind. Update your browser and your computer to be sure. Mac command-line tools still need a future Apple update.
| App | Device | Affected | Fixed in |
|---|---|---|---|
| Mozilla Firefox | Windows, Mac, Linux | Firefox with settings that stopped the automatic block | 158.0.1 (ESR: 153.5.1 or 115.43.1)[1] |
| Google Chrome | Windows, Mac, Linux | Chrome that has not yet received the Oct 27 trust-list update | Chrome blocked the keys the same day with no update. It removes the whole root certificate in a release that began rolling out Oct 27, 2026.[2] |
| Microsoft Edge | Windows, Mac | Edge that has not yet received the Oct 27 trust-list update | Microsoft Edge blocks the keys automatically. Microsoft planned to remove the affected roots from Edge's trust list on Oct 27, 2026.[4] |
| Windows 10 and 11 | Windows | Windows without Microsoft's Oct 26, 2026 trust-list update | Microsoft released an out-of-band Windows update on Oct 26, 2026 that removes seven affected certificates.[4] |
| macOS | Mac | Mac command-line tools (not Safari or other apps) | Apple blocked the certificates automatically from Oct 19, 2026 (and the root on Oct 23). A future macOS update will block them in command-line tools too.[3] |
| Tailscale | Windows, Mac, Linux | Tailscale older than v1.104.2 | 1.104.2[7][5] Tailscale v1.104.2 (Oct 21, 2026) includes Go 1.27.3, which refuses the compromised certificates. |
How to check your version
These checks only look. They do not change anything on your computer.
Google Chrome on Windows
Easy way: Click the three dots at the top right > Help > About Google Chrome. Chrome checks for updates there, then click Relaunch.
Or type this in PowerShellRead-only. It only reads the version and changes nothing.
(Get-ItemProperty 'HKCU:\Software\Google\Chrome\BLBeacon' -ErrorAction SilentlyContinue).version
Google Chrome on Mac
Easy way: Chrome menu bar: Chrome > About Google Chrome.
Or type this in TerminalRead-only. It only reads the version and changes nothing.
defaults read "/Applications/Google Chrome.app/Contents/Info" CFBundleShortVersionString
Google Chrome on Linux
Easy way: Chrome menu: three dots > Help > About Google Chrome.
Or type this in TerminalRead-only. It only reads the version and changes nothing.
google-chrome --version
Mozilla Firefox on Windows
Easy way: Click the three lines at the top right > Help > About Firefox. Firefox checks for updates there.
Or type this in PowerShellRead-only. It only reads the version and changes nothing.
Get-ItemProperty 'HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*','HKLM:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*','HKCU:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*' -ErrorAction SilentlyContinue | Where-Object DisplayName -like '*Mozilla Firefox*' | Select-Object DisplayName,DisplayVersion
Mozilla Firefox on Mac
Easy way: Firefox menu bar: Firefox > About Firefox.
Or type this in TerminalRead-only. It only reads the version and changes nothing.
defaults read "/Applications/Firefox.app/Contents/Info" CFBundleShortVersionString
Mozilla Firefox on Linux
Easy way: Firefox menu > Help > About Firefox.
Or type this in TerminalRead-only. It only reads the version and changes nothing.
firefox --version
Microsoft Edge on Windows
Easy way: Click the three dots at the top right > Help and feedback > About Microsoft Edge.
Or type this in PowerShellRead-only. It only reads the version and changes nothing.
(Get-Item "${env:ProgramFiles(x86)}\Microsoft\Edge\Application\msedge.exe" -ErrorAction SilentlyContinue).VersionInfo.ProductVersionMicrosoft Edge on Mac
Easy way: Edge menu bar: Microsoft Edge > About Microsoft Edge.
Or type this in TerminalRead-only. It only reads the version and changes nothing.
defaults read "/Applications/Microsoft Edge.app/Contents/Info" CFBundleShortVersionString
Windows 10 and 11 on Windows
Easy way: Start > Settings > Windows Update. Then click Update history to see recent updates.
Or type this in PowerShellRead-only. It only reads the version and changes nothing.
Get-CimInstance Win32_OperatingSystem | Select-Object Caption,Version,BuildNumber; Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5 HotFixID,InstalledOn
macOS on Mac
Easy way: Apple menu > About This Mac. Or Apple menu > System Settings > General > Software Update.
Or type this in TerminalRead-only. It only reads the version and changes nothing.
sw_vers -productVersion
Tailscale on Windows
Easy way: Click the Tailscale icon (tray on Windows, menu bar on Mac) and choose About Tailscale.
Or type this in PowerShellRead-only. It only reads the version and changes nothing.
tailscale version
Tailscale on Mac
Easy way: Click the Tailscale icon in the menu bar > About Tailscale.
Or type this in TerminalRead-only. It only reads the version and changes nothing.
tailscale version
Tailscale on Linux
Easy way: Open the app and look in its Help or About menu, or check your software manager.
How to fix it
- Update your browser: Chrome (three dots > Help > About Google Chrome), Firefox (three lines > Help > About Firefox), Edge (three dots > Help and feedback > About Microsoft Edge).
- Run Windows Update (Settings > Windows Update) and install everything, including the update from Oct 26.
- On a Mac, run Software Update (System Settings > General > Software Update).
- If you use Tailscale, update it to the newest version.
- A site that suddenly shows a certificate warning might use the blocked company. That is expected. Do not click through the warning. Tell the site owner.
More on each app: Is my Chrome up to date?, Is my Firefox up to date?, Is my Edge up to date?, Is my Windows up to date?, Is my Mac up to date?, Is my Tailscale up to date?
Official links
- Mozilla: blog post about the eMudhra block
- Apple: about the compromised eMudhra certificates
- Microsoft: response to the eMudhra keys
Check before installing, and only use these official links or the app's own update button.
For AI agents
This page as data: /incidents/emudhra-fake-website-certificates.json. All problems: /feed.json. Use read-only checks only, and ask before installing anything.
Tracking numbers (CVE): None
Sources
- MakerMozilla Security Blog: Protecting Firefox users after the eMudhra compromise (Oct 20, 2026)
- MakerGoogle: Protecting Chrome and Android users from compromised eMudhra certificates (Oct 20, 2026)
- MakerApple Support: About the compromised eMudhra intermediate CAs (Oct 23, 2026)
- MakerMicrosoft MSRC: Response to compromised eMudhra keys (Oct 26, 2026)
- MakerTailscale changelog (Oct 21, 2026 entry) (Oct 21, 2026)
- Official noticeeMudhra: Statement on the certificate security incident (Oct 21, 2026)
- MakerTailscale security bulletin TS-2026-013 (eMudhra certificates) (Oct 21, 2026)
"Maker", "CISA", "NVD", "GitHub advisory" and "Official notice" are official sources. "Researcher" and "News" are extra context.