How to Resolve SEC_ERROR_REUSED_ISSUER_AND_SERIAL in Firefox?

What is SEC ERROR REUSED ISSUER AND SERIAL in Firefox?

SEC_ERROR_REUSED_ISSUER_AND_SERIAL is a specific error in Mozilla Firefox that indicates a problem with the SSL/TLS certificate being presented by a website.

This error occurs when Firefox detects that the certificate has a reused issuer and serial number combination, which is not allowed according to the SSL/TLS protocol standards.

Common Causes

Issuer Error

Issuer Error is a situation where CA, which is responsible for providing SSL/TLS certificates concerned, reissues the same certificate for one web site for another web site that is quite unrelated.

Such kinds of mistakes are usually caused by negligence or procedural problems within the working of the CA.

This should be so because when a CA issues a certificate the serial number and issuer information should be unique. If they try to use the same serial number in the same certificate with a different name of the issuer, browsers i.e Firefox will alert the user.

The reuse can cause confusion in SSL/TLS handshakes, which may result in failed secure connection or even enable eavesdropping on data.

This error again emphasizes on some quality measures that need to be applied within CAs so that each certificate that is issued is unique and correlates to the domain it is to be associated with.

Compromised

Compromised CA scenarios are among the most critical security breaches in the SSL/TLS ecosystem. The private key of a CA is a highly sensitive piece of data that must remain secure at all times.

If a CA’s private key is compromised, attackers can create and issue their own certificates that appear to be legitimately signed by the CA.

Also Read: How to Fix the SEC_ERROR_UNKNOWN_ISSUER Error in Firefox?

These fake certificates can then be used to impersonate any website, decrypt the traffic and data from the users, or perform a phishing attack without eliciting any usual security warnings in browsers.

It has an arguably larger scale impact since those relying on the CA’s certificates, whether a website or an online service, are also at risk of being compromised.

To avoid such risks, CAs must adopt stringent security controls such as the hardware security module, the strict access to the CA key, audits for unauthorized activities among others.

Weak Issuer Practices

Weak Issuer Practices are observed when a CA is not thorough in verifying the domain ownership before it issues a certificate. The validation process is aimed at checking whether the entity applying for the certificate really owns this particular domain.

In case this process is not well followed, then people or organizations that are not supposed to have certificates of membership will be issued with certificates hence posing a security risk.

For instance, an attacker can acquire a genuine SSL certificate for a domain that they do not have any association with ; thereby performing MITM attacks, phishing scams, and other related actions that appear to be certified.

The best practices in issuance of certificates include confirming the ownership by domain means such as DNS records, emails or even physical documents in order to avoid issuing certificates to wrong entities.

Domain Sharing

Domain sharing is a process where a single SSL/TLS certificate as well as the linked private key is utilized on distinct subdomains or even on a variety of domain names that belong to the same organization.

There is no doubt that this can greatly aid certificate management and decrease costs; however, it is coupled with great security threats.

In the case when one of the domains or subdomain becomes malicious, the attacker can use the certificate and key issued for all domains, to impersonate himself as any of the other domains in the same certificate.

Furthermore, having the certificates and private keys on multiple servers or domains makes them vulnerable; an attacker is likely to breach into it and get access to the private key.

In general, it is inadvisable to combine external domains and subdomains or to use wildcard or SAN certificates only when really necessary, and only if their usage is restricted in some way.

Server Misconfiguration

Server Misconfiguration involves scenarios where the web server is set up incorrectly, leading to the wrong SSL/TLS certificate being used for a domain.

This can happen due to human error during server setup or updates, such as when an administrator mistakenly assigns the wrong certificate to a domain or fails to properly configure the server to handle multiple domains.

For instance, if a web server is serving numerous websites (this is virtual hosting), it needs to be configured properly so that every website is using the proper SSL/TLS certificate.

Otherwise, users to the site could be served with a certificate not associated with the domain name that they are attempting to reach, leading to browser warnings or dropped connections.

In more critical scenarios, it also exposes users to man-in-the-middle attacks if the attackers exploit the misconfiguration.

Captive Portals

Captive Portals are normally located in the public Hot-spot locations like airports, cafes, and hotels among others. The majority of free available networks direct the users to a payment or login page, otherwise referred to as the captive portal.

In order to achieve this, the network may issue a recycled SSL/TLS certificate to all the users irrespective of the requested domain.

This makes the certificates used multiple times by different users and sessions, going against the requirement of having unique certificates.

Also, since such certificates are self-signed or not verified, they will trigger security warnings in browsers.

Captive portals are in place to control access to the public network but are in themselves a security risk. Particularly if the reused certificate itself is under attack or if users are tricked into authenticating an imposter certificate presented to them by a network-controlling attacker.

Customers have to be careful when they are connected to a public Wi-Fi, while operators also have to employ good security infrastructure to limit harm.

How to Fix SEC ERROR REUSED ISSUER AND SERIAL in Firefox?

Remove Firefox Certificates

The first way is to flush the Firefox certificate cache. This forces the browser to re-download new certificates from the site once again. This is useful when the browser cached an incorrect or outdated certificate. This is how you can do it:

Step 1: Launch the Firefox browser and navigate to about:preferences#privacy. This will take you to the Privacy & Security options.

Step 2: Go down to the “Certificates” section and select the “View Certificates” button. It will display the Certificate Manager.

Step 3: Go to Certificate Manager and click on the “Authorities” tab. There, you will find a list of Certificate Authorities (CAs) that have issued certificates stored by Firefox.

Step 4: Locate the CA that issued the offending certificate. When you locate it, select the CA and then click the “Delete or Distrust” button.

Step 5: Make sure you want to delete all certificates for that issuer. This will delete the cached certificates and any possible duplicates that could be the source of the error.

Step 6: Close and reopen the Firefox browser again, and attempt to visit the site again. By deleting the outdated certificates and forcing Firefox to ask for a new certificate, any issues resulting from old or duplicate certificates should be eliminated, if the CA has fixed the issue on their end.

Disable Security Exception

If you had previously added a security exception for the website which had produced the error in Firefox, this exception may be responsible for the error continuing to occur. Deleting the security exception will have Firefox re-evaluate the certificate without bypassing its security checks.

Step 1: Navigate to about:preferences#privacy and choose “View Certificates“.

Step 2: Navigate to the “Servers” tab in the Certificate Manager. You have a list of domains for which you’ve added security exceptions.

Step 3: Locate the offending domain which triggers the SEC_ERROR_REUSED_ISSUER_AND_SERIAL error.

Step 4: Choose the domain and click on “Delete or Distrust” to delete the security exception.

Step 5: Re-start Firefox and try to access the website again. Because you are removing the exception, Firefox will be considering the connection as new and will once again check for the uniqueness and integrity of certificates.

This approach is effective if the issue was due to a reused certificate that was already accepted.

Use Firefox’s Private Browsing Mode

Firefox private browsing mode will create a new browsing session which will not use any information cached, such as cached certificates. It’s an easy way to check quickly if stored certificates are the cause of your error within a regular browsing session.

Step 1: Launch Firefox and select “New Private Window“. You can access it from the main menu or use Ctrl + Shift + P.

Step 2: Visit the website that contains this error in the private browsing window.

Step 3: Private browsing doesn’t cache data, so Firefox will establish a new connection and will be supplied with new certificates. If your problem was with the cached certificates in your normal session, the page will load as usual.

This technique allows you to quickly visit the page or see if the error occurs only on your session. But if the error still occurs in private mode, it may be a more involved issue, e.g., a server issue or a CA issue.

Attempt to switch off HTTPS Only Mode

Firefox’s HTTPS-Only feature ensures that you access all sites via secure connections. It denies any insecure HTTP requests. That is secure but will deny access to some sites with broken or expired certificates.

Step 1: Enter about:config in the Firefox address bar and press Enter. This will reveal the advanced settings.

Step 2: In the search box, enter security.https_only_mode.

Step 3: Upon viewing the setting, modify its value to false by either double-clicking on it or by clicking on the toggle button.

Step 4: Restart Firefox and attempt to reload the site. Disabling HTTPS-Only mode might allow you to view the site using an HTTP connection, which might prevent you from seeing the reused certificate issue for a short amount of time.

Remember that this is only a quick solution, as opening up non-encrypted connections compromises your overall security. It might be useful when resolving issues, but not for secure surfing. 

Use a Different Browser

Attempt to go to the site using another internet browser such as Google Chrome or Microsoft Edge. Various browsers check SSL/TLS certificates differently, and so the site may function normally using another browser.

Step 1: Launch Google Chrome or Microsoft Edge.

Step 2: Access in incognito or private mode to prevent access to data from previous sessions.

Step 3: Attempt to load the website in a different web browser.

This method might be capable of making you temporarily secure from the SEC_ERROR_REUSED_ISSUER_AND_SERIAL error, but it is not safe to use to retrieve sensitive information since the root certificate problem still persists.

You can use this approach only as a stopgap or to collect non-sensitive data.

Contact the Site Owner

The optimal solution is that the owner of the website would fix the primary issue with the certificate. This is most typically achieved by obtaining a new certificate with a new serial number and ensuring that the certificate chain is proper.

Step 1: Reach out to the administrator or technical support of the site. Let them know about this error, the issuer details, and the domain name.

Step 2: Have the owner of the website call their Certificate Authority (CA) and ask it to issue a new certificate. The CA will use the best practices in the industry to ensure that the new certificate will have a different serial number and be properly configured.

Step 3: Once the website owner has renewed the certificate, test the site on Firefox once more. If the server-side certificate issue has been fixed, the site should now be able to open securely without an issue.

Report Problems to Mozilla

If you believe the issue is that a Certificate Authority wrongly issued a certificate, you can report it to Mozilla. Mozilla maintains a list of trusted Certificate Authorities and can act on it.

Step 1: Gather data such as the domain names affected, the Certificate Authority name, and error messages pertinent.

Step 2: Send an email to [email protected] with what you discovered. Describe the problem and why you believe the CA may have inadvertently issued duplicate or reused certificates.

Step 3: Mozilla’s security team will take the issue into account and can act, for instance, removing the trust from the bad CA or assisting them to correct the issue.

Reporting the problem to Mozilla maintains the SSL/TLS system secure by keeping Certificate Authorities in check.

Disable Firefox Certificate Verifications

If you have to, you can turn off SSL/TLS certificate verification in Firefox. This will let sites using reused certificates load. But this will greatly reduce your security and should only be done on a temporary basis and with carefulness.

Step 1: In the address bar of Firefox, enter about:config and press Enter.

Step 2: Search for security.tls.version.enable-deprecated and set its value to true.

Step 3: Then, find security.ssl.enable_ocsp_stapling and set its value to false. This disables Online Certificate Status Protocol (OCSP) stapling, which verifies certificates to determine if they are valid or not.

Step 4: Last but not least, search for security.cert_pinning.enforcement_level and configure it to 0. This disables certificate pinning enforcement, which is a feature to ensure that only authentic and trusted certificates are accepted.

Step 5: Close Firefox and attempt to revisit the offending site. You will probably notice warnings of unsafe connections, which you can disregard. Disabling these security features makes it easier for your browser to be attacked and should only be done temporarily, if at all. It should be enabled again after fixing the problem.

Conclusion

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