How to Fix SEC_ERROR_REUSED_ISSUER_AND_SERIAL in Firefox

Running into an SSL error while browsing can be frustrating, especially when you’re dealing with cryptic messages like SEC_ERROR_REUSED_ISSUER_AND_SERIAL in Firefox. This error stops you from accessing a website, often without a clear explanation of what went wrong. If you’re managing a local development server, working with internal networks, or dealing with a website’s SSL configuration, this issue can disrupt your workflow.

In this guide, we’ll break down what causes the error, why Firefox blocks these connections, and, most importantly, how to fix it. Whether you’re a developer, system administrator, or just trying to access a site, follow these steps to resolve the issue and restore secure browsing.

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What is the SEC_ERROR_REUSED_ISSUER_AND_SERIAL Error in Firefox?

The SEC_ERROR_REUSED_ISSUER_AND_SERIAL error occurs when Firefox detects that a website’s SSL certificate has a duplicate serial number issued by the same certificate authority (CA).

Every SSL certificate must have a unique serial number. If two certificates from the same issuer share the same serial number, Firefox sees it as a potential security risk and blocks the connection. This error is common in environments where self-signed certificates, internal certificate authorities, or misconfigured SSL setups are used.

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What Causes the SEC_ERROR_REUSED_ISSUER_AND_SERIAL Error?

Let’s explore more in-depth what triggers this error before fixing it.

1. Duplicate Certificate Serial Numbers: If a certificate authority (CA) issues two different certificates with the same serial number, Firefox will reject one of them. This issue often happens in internal networks using self-signed or enterprise-issued certificates.
2. Improper Certificate Renewal or Replacement: If a website replaces its SSL certificate but retains the same serial number as the old one, Firefox will flag it as an error. This is common when manually generating or renewing certificates.
3. Cached SSL Certificates in Firefox: Sometimes, Firefox may store outdated SSL certificates, causing conflicts when a new one is issued. This happens when websites update their certificates without properly revoking old ones.
4. Self-Signed Certificates in Local Environments: Developers often use self-signed certificates for local testing. If a new self-signed certificate is issued but reuses an existing serial number, Firefox will block it.
5. Enterprise or Custom Certificate Authorities (CAs): Organizations managing their own internal CA may encounter this issue when reissuing certificates without updating the serial numbers.

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How to Fix the SEC_ERROR_REUSED_ISSUER_AND_SERIAL Error?

Fixing this error depends on whether you are a website administrator, developer, or regular user. Follow the steps below based on your situation.

1. Delete the Problematic Certificate from Firefox

If a website’s certificate has been updated but Firefox still recognizes an old version with the same serial number, clearing it from Firefox’s certificate storage can resolve the error. Here are the steps to delete the certificate:

1. Open Firefox and type about:preferences#privacy in the address bar.
2. Scroll down to the Certificates section and click View Certificates.
   
   
   
   
3. Under the Authorities or Servers tab, find the certificate related to the problematic site.
   
   
   
   
4. Select it and click Delete or Distrust.
5. Restart Firefox and try accessing the site again.

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2. Remove the Old Certificate from Your System

If you’re using an enterprise or self-signed certificate, it may also be stored at the system level. Removing and reinstalling the correct certificate can fix the issue.

For Windows Users:

1. Press Win + R, type certmgr.msc, and hit Enter.
2. In the Certificate Manager, go to Trusted Root Certification Authorities > Certificates.
   
   
   
   
3. Look for the certificate related to the problematic website, right-click it, and select Delete.
4. Restart Firefox and try again.

For Mac Users:

1. Open Keychain Access (search for it in Spotlight).
2. Navigate to System > Certificates.
   
   
   
   
3. Find the problematic certificate, right-click it, and select Delete.
4. Restart Firefox and retry the site.

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3. Regenerate the SSL Certificate (For Developers & Site Admins)

If you’re managing your own SSL certificates, regenerating a new one with a unique serial number can solve the problem. For OpenSSL Users:

1. Generate a new private key:
   
   openssl genrsa -out newkey.pem 2048
   
2. Create a new certificate signing request (CSR):
   
   openssl req -new -key newkey.pem -out newcsr.csr
   
3. Generate a new self-signed certificate with a unique serial number:
   
   openssl x509 -req -days 365 -in newcsr.csr -signkey newkey.pem -set_serial 01 -out newcert.pem

Replace the old certificate with the newly generated one and restart your web server. Check our article discussing OpenSSL and its commands for efficient certificate management.

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4. Disable HTTPS Scanning in Antivirus Software

Some antivirus programs, such as Avast or Kaspersky, intercept SSL connections. As a result, Firefox detects duplicate serial numbers. Temporarily disabling HTTPS scanning in your antivirus settings may resolve the issue. To disable HTTPS scanning (for example, on Avast), follow the steps below:

1. Open Avast and go to Settings.
2. Navigate to Protection > Core Shields.
3. Scroll down to Web Shield and uncheck Enable HTTPS Scanning.
4. Restart Firefox and check if the error persists.

Other antivirus programs should have similar settings and solutions for disabling HTTPS.

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Get a Secure, Error-Free SSL Setup

The SEC_ERROR_REUSED_ISSUER_AND_SERIAL error is a direct result of SSL certificate mismanagement. Whether dealing with duplicate serial numbers, self-signed certificates, or internal CA conflicts, having a properly issued SSL certificate eliminates these issues.

Instead of troubleshooting SSL errors, invest in a reliable SSL certificate from a trusted provider. SSL Dragon offers a wide range of certificates that ensure security and seamless compatibility with all browsers, including Firefox. Browse our selection today and secure your website correctly without the hassle of technical errors.