How to troubleshoot Firefox SEC_ERROR_UNKNOWN_ISSUER?

By ivan.diskin | March 25, 2019 |

greater than 5 minutes

Occasionally, when trying to open specific websites using the Firefox browser, you might see the “Your connection is not secure” error page. The error code is given as “SEC_ERROR_UNKNOWN_ISSUER”, and Mozilla Firefox denies you access to the website. To help you get through, this article explains how to fix the SEC_ERROR_UNKNOWN_ISSUER problem.

What Does Error Code: SEC_ERROR_UNKNOWN_ISSUER Mean?

Before connecting to a website, Mozilla Firefox must establish if the website is secure or not. To do this, the website you’re trying to access must provide a certificate, which is normally issued by a certificate authority. This is to confirm that the connection is encrypted and that the user is connected to the intended website.

If Firefox cannot validate the certificate or the encryption doesn’t meet Mozilla Firefox’s security requirements, the browser blocks the connection and instead displays the error message SEC_ERROR_UNKNOWN_ISSUER.

Why Does the Error Occur?

Secure Sockets Layer (SSL) is a type of technology that keeps your internet connection safe and away from the prying eyes of hackers. This technology uses sophisticated encryption algorithms that make your personal information impossible to read. It’s the security system used by most banks and online shopping stores among millions of other websites that want to safeguard the personal details of their consumers and visitors.

Typically, a website whose URL starts with HTTPS (Hypertext Transfer Protocol Secure) means that all the data is encrypted. However, when the websites that use the SSL certificate are blocked, it may indicate that a virus or malware infection is intercepting your internet connection and replacing legitimate certificates with its own. As a result, Firefox is unable to trust these certificates and therefore blocks you from accessing such sites.

This is especially true when the error code SEC_ERROR_UNKNOWN_ISSUER appears on multiple sites. Other reasons why the error occurs include:

  • corruption in the Windows Registry due to the installation or uninstallation of Firefox-related software,
  • an incomplete download or installation of Firefox-related software,
  • wrongful deletion of Firefox-related files by one of your programs.

How to Resolve the Mozilla Firefox “SEC_ERROR_UNKNOWN_ISSUER” Error?

Fix 1: Perform a Full Malware Scan

The chances that the “SEC_ERROR_UNKNOWN_ISSUER” error occurred due to a malware infection are high. Hackers develop sophisticated malicious codes that intrude into your system to damage, corrupt or delete important Firefox-related files with the aim of creating backdoors to your personal information. Likewise, malware can try to inject fake certificates and make them appear as legit.

To get rid of destructive entities, you need a program that’s specifically designed to detect the different kinds of malicious software. We recommend using Auslogics Anti-Malware for total protection against these intruders. This software not only detects the malware items wreaking havoc on your system but also gives you the option to quarantine them.

This is especially helpful where you know that one of your programs is safe but the malware removal tool finds it to be suspicious. You can also add the program to the excluded files and folders list to prevent it from being scanned.

Auslogics Anti-Malware will scan your entire Windows system and remove the malware from wherever it’s hiding. After the scan is complete, restart your system and try to access the website that conveyed the “SEC_ERROR_UNKNOWN_ISSUER” error message.

Fix 2: Enable “Auto-Detect Proxy” and Refresh Mozilla Firefox

  1. Launch Firefox and press the “Menu”, located at the top-right corner of the browser.
  2. Go to “Options”.
  3. Scroll down to the bottom of the page and select “Settings” under the “Network Settings” section.
  4. Select “Auto-detect proxy settings for this network”.
  5. Click “OK” and then restart Firefox.

If this doesn’t fix the “SEC_ERROR_UNKNOWN_ISSUER” error code, you can try to refresh Firefox.

To Refresh Firefox:

  1. Open the Mozilla Menu, and select “Help”.
  2. Select “Troubleshooting Information”.
  3. On the right side of the window that opens, click the “Refresh Firefox” button.

This option gives you an up-to-date Firefox. Hopefully, this should take care of the “Your connection is not secure” error. If it doesn’t, proceed to Fix 3 below.

Fix 3: Disable SSL3 Connections

  1. Launch Firefox and type “about:config” in a new tab.
  2. Select the “I accept this risk!” button.
  3. Wait for the list to be populated, and then type SSL3 in the “Search” box.
  4. Find and select “security.ssl3.dhe_rsa_aes_128_sha” and “security.ssl3.dhe_rsa_aes_256_sha”, and then change their values from “true” to “false”.

Restart Firefox and check if the error still appears when trying to access your websites.

Fix 4: Change the Value of the ‘security.enterprise_roots.enabled’

  1. On a new tab in Firefox, type “about:config”.
  2. Next, click the “I accept the risk!” button.
  3. When the list is populated, type roots in the search box.
  4. Find “security.enterprise_roots.enabled in the list and double-click it.
  5. Next, change the value to “false”.
  6. Refresh Firefox using the steps outlined above.

You should now be able to browse any site using your Firefox browser without any issues.

Fix 5: Run Windows System File Checker

When it comes to restoring corrupt or missing system files, System File Checker (SFC) is a handy Windows utility tool that you should use. To proceed:

  1. Press the Windows Key and start typing command prompt.
  2. Right-click “Command Prompt” from the results, and choose “Run as administrator”.
  3. Select “Yes” when prompted to gain administrator privileges.
  4. Next, type sfc /scannow, and press “Enter”.
  5. Windows will scan the system files and fix any problematic or missing files associated with the SEC_ERROR_UNKNOWN_ISSUER problem.

The above solutions apply when you encounter the “Your connection is not secure” issue on multiple websites. However, if the error affects only one site, then you can try the following fixes:

Fix 6: Add an Exception for the Single Website

Before you proceed, you should understand that bypassing a security warning jeopardizes your internet connection and makes your system vulnerable to exploits. You should, therefore, proceed at your own risk.

  1. Open the website that’s giving you the error code: SEC_ERROR_UNKNOWN_ISSUER.
  2. Click “Advanced” on the warning page.
  3. Select “Add Exception”.
  4. Choose the “Confirm Security Exception” option in the window that pops up next.

This enables you to access the website without problems.

Fix 7: Create a New User Profile

If you’re still getting the “Your connection is not secure” error message with the error code: SEC_ERROR_UNKNOWN_ISSUER, you can try to create a new administrator account.

  1. First, exit Mozilla Firefox.
  2. Press the Windows Key+R simultaneously and type firefox.exe –p in the “Run” dialog.
  3. Press “Enter” or click “OK”.
  4. Select “Create Profile” in the “Firefox – Choose User Profile” window.
  5. Follow the prompts and when you’re done, restart Firefox.
  6. Log in with your new account details and try to open the troublesome website to see if the issue has been resolved.

We hope you find the above information on how to fix the SEC_ERROR_UNKNOWN_ISSUER problem helpful. If you tried other solutions and they worked, you are welcome to share with our community in the comments section below.

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