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Summary :


When opening a web page in Firefox, you may receive the error code: SEC_ERROR_UNKNOWN_ISSUER. This indicates that the website is using an SSL certificate that was issued by an untrusted entity. In this article, MiniTool Solution offers some possible and useful solutions to help you out.


When using Firefox to visit a website, this browser will verify the certificate used by the website is valid. If it cannot be validated, Firefox can disconnect the connection to the web page. Usually, you get an error message showing “your connection is not secure” with the error code sec_error_unknown_issuer. Sometimes you see the message “warning: potential security risk ahead” with the same error code.

sec error unknown issuer

This error code means the certificate is not unknown by Firefox and therefore it cannot be trusted by default. Additionally, if your computer is infected by malware or virus, it is likely that you also come across this error.

So, how can you fix the error code? Here is something you can do!


Option 1: Run a Virus Scan

If a virus is preventing the certificate from being detected, the error code may occur. Thus, running a virus scan for your entire Windows system could be helpful. Just try Windows Defender if you are running Windows 10. If this cannot detect the virus, try another antivirus program like Malwarebytes.

After the scan, remove the virus. Restart your PC and open the website again to see if SEC_ERROR_UNKNOWN_ISSUER is solved.

Option 2: Disable the Interception of Secure Connections

If you have installed a third-party antivirus program on your computer before, perhaps the issue is caused by the software since it can interfere with Firefox's secure connections. You should uninstall the third-party software and use the security software offered for Windows by Microsoft, for example, Microsoft Security Essentials (for Windows 7) and Windows Defender (Windows 10/8).

If you don’t want to uninstall the software, just reinstall it. This may let the software place its certificate to the Firefox trust store again.

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In addition, you can disable the SSL scanning in your security software. Take Avast as an example.

  1. Go to the dashboard of Avast.
  2. Navigate to Menu > Settings > Protection > Core Shields.
  3. Scroll down to Configure shield settings, go to Web Shield and ensure the Enable HTTPS scanning option is not selected.

uncheck enable HTTPS scanning

Option 3: Contact the IT Department

Some traffic filtering or monitoring products may replace a webpage’s certificate with their own to intercept encrypted connections and trigger errors on secure sites like SEC_ERROR_UNKNOWN_ISSUER. If you doubt about this case, contact the IT department to make sure the Firefox configuration is correct.

Option 4: Verify That the Site Is Configured Correctly

When the error code: SEC_ERROR_UNKNOWN_ISSUER appears, you can click Advanced. If you get one message as follows:

  • The certificate is not trusted because the issuer certificate is unknown.
  • The server might not be sending the appropriate intermediate certificates.
  • An additional root certificate may need to be imported.

This indicates the site misses the intermediate certificate. In this case, you can enter the website address into a third-party tool like the SSL Labs test page, to verify that the site is configured correctly.

If you get “Chain issues: Incomplete”, no proper intermediated certificate exists. So, contact the owners of the web page and tell them this issue.

Option 5: Bypass the Warning

You may see the message after clicking Advanced – “the certificate is not trusted because it is self-signed”. This indicates the web site has a self-signed certificate.

By default, this certificate that wasn’t issued by a recognized certificate authority is not trusted since it doesn’t show who is the recipient of the data.

In this case, you can bypass the warning by clicking Accept the Risk and Continue on the “potential security risk ahead” page. If you have the issue - Firefox your connection is not secure SEC_ERROR_UNKNOWN_ISSUER, click Add Exception.

add security exception

The End

Here are possible solutions to SEC_ERROR_UNKNOWN_ISSUER in Firefox. If you are bothered by this error code when visiting a web site, just follow these methods mentioned above to get rid of the trouble.

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