Certificate contains the same serial number as another certificate

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You may see the following error message when attempting to access a router's configuration page:

Your certificate contains the same serial number as another certificate issued by the certificate authority. Please get a new certificate containing a unique serial number. (Error code: sec_error_reused_issuer_and_serial)

This article describes the cause of this problem and how to work around it.


Cause

Older routers will sometimes improperly regenerate their security certificates instead of keeping the same one for the life of the device. If you have added a permanent security exception for your router, and if this regeneration is done improperly, Firefox will detect the change as a possible attack.


Solution

The long term solution is to contact your hardware vendor and see if updates are available for your device which fix this problem.


Workaround

If you are confident that no attack has occurred, you can work around the problem by deleting your old exception and using temporary exceptions for subsequent visits to the page:

To delete your old exception:

  1. At the top of the Firefox window, click on the Firefox button and then select Options.At the top of the Firefox window, click on the Tools menu and then select Options.On the menu bar, click on the Firefox menu and select Preferences....At the top of the Firefox window, click on the Edit menu and select Preferences.

    Click the menu button New Fx Menu and choose Options.Preferences.

  2. Select the Advanced panel.
  3. Click on the Encryption tab.
  4. Click View Certificates to open the Certificate Manager window.
  5. In the Certificate Manager window click on the Servers tab.
  6. Find the item that corresponds to the site that generates the error. Note the Certificate Authority (CA) for that server - the CA name appears above the site name.

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  7. Click on the server certificate that corresponds to the site that generates the error and press Delete....
  8. Click OK when prompted to delete the exception.
  9. Click on the Authorities tab.
  10. Click on the item that corresponds to the CA that you noted earlier and then press Delete....
  11. Click OK when prompted to delete the exception.
  12. Click OK close the Certificate Manager window.

  13. Click OK to close the Options window.Click Close to close the Preferences window.Close the Preferences window. Close the about:preferences page. Any changes you've made will automatically be saved.

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To add a temporary exception to allow access to the page:

  1. When you go to the page, you will be presented with an error. Click on the Or you can add an exception... link at the bottom of the error.
  2. Click on Add Exception... to open the Add Security Exception window.
  3. Click Get Certificate to fill in the Certificate Status section of the Add Security Exception window.
  4. Click to un-check the Permanently store this exception item.
  5. Click Confirm Security Exception to close the Add Security Exception window.
  1. When you go to the page, you will be presented with an error. Click on the I Understand the Risks link at the bottom of the error, then click Add Exception....
  2. Click on Add Exception... to open the Add Security Exception window.
  3. Click Get Certificate to fill in the Certificate Status section of the Add Security Exception window.
  4. Click to un-check the Permanently store this exception item.
  5. Click Confirm Security Exception to close the Add Security Exception window.

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