Certificate Lifecycle Management Reading Time: 6 minutes

All you need to know about Wildcard Certificates

What is Wildcard Certificate?

A wildcard certificate, also known as a wildcard SSL certificate, is a type of digital certificate used to secure multiple subdomains of a single domain.

Wildcards are frequently used in Secure Socket Layers (SSL) certificates to extend SSL encryption to subdomains. A traditional SSL certificate is only valid for a single domain, such as www.abc.com. A *.abc.com wildcard certificate can protect all the subdomains under one domain, e.g., cloud.abc.com, shop.abc.com, mobile.abc.com, and other domains.

The asterisk (*) is used as the wildcard character in the certificate. It can represent any single subdomain level. For example, if you have a wildcard certificate for *.abc.com, it will work for any subdomain like finance.abc.com, maketing.example.com, etc.

Wildcard certificates are particularly useful for organizations with numerous subdomains that want to secure them all under a single certificate. They provide encryption and authentication for data transmitted between the user’s browser and the web server, enhancing the security and privacy of web communications. However, it’s essential to manage wildcard certificates carefully because if the private key is compromised, an attacker could potentially use it to impersonate any subdomain under the wildcard domain. Therefore, proper security practices, such as safeguarding the private key and regularly renewing certificates, are crucial when using wildcard certificates.

Issues with Wildcard Certificates

There are a few major security issues with the widespread use of wildcard certificates.

  1. False Sense of Security

    In high-security systems, for example: ‘https://cloud.abc.com’ or ‘https://personnel_records.abc.com,’ it’s crucial to specify their names explicitly. Wildcard certificates might give a false sense of security, as they don’t guarantee that users are genuinely accessing the intended systems. Users could unknowingly connect to outdated or inactive links or servers that no longer serve any purpose. Using wildcards conceals potential server and DNS errors.

  2. Misuse of Certificates and its associated private keys

    Using wildcard certificates significantly increases the risk of the certificate falling into the wrong hands. Improperly configured wildcard certificates can lead to security vulnerabilities. If they are not correctly set up or their private keys are exposed, attackers could exploit them. This is primarily because wildcard certificates like ‘*.abc.com’ will likely be extensively deployed across various systems, including high-security accounting systems, phone books, routers, and load balancers.

    It’s a matter of basic probability: the more individuals involved in installing the same wildcard certificate, the greater the likelihood of it being compromised or leaked. In contrast, named certificates are installed and managed exclusively during designated teams’ setup of specific systems. This approach offers enhanced accountability by a significant margin. Moreover, named Subject Alternative Name (SAN) certificates can only be utilized on designated SAN devices, ensuring error-free connections.”

    1. Security Concerns

      If the private key of a wildcard certificate is compromised, it can potentially be used to impersonate any subdomain under the wildcard domain. This makes it essential to protect the private key rigorously.

    2. Limited to a Single Level

      Wildcard certificates only cover one level of subdomains. For example, a certificate for *.abc.com would secure subdomains like blog.abc.com and mail.abc.com but not subdomains like sub.blog.abc.com. To secure multiple levels of subdomains, you would need a multi-level wildcard certificate, which can be more expensive and less commonly available.

    3. Complexity for Third Parties

      Some third-party services or applications may not support wildcard certificates or may require additional configuration. Compatibility issues may arise in certain situations.

    4. Risk of Overuse

      Temptation to use wildcard certificates for too many subdomains, potentially increasing the risk if the private key is compromised. It’s essential to limit the use of wildcard certificates to only those subdomains that genuinely need it.

  3. Certificate Revocation

    Revoking a wildcard certificate can be more complex than revoking individual certificates. Revocation typically applies to the entire wildcard domain, affecting all subdomains.

Recommendations for Wildcard Certificate Policies

Wildcard certificates can be a convenient solution for securing multiple subdomains within an enterprise-level organization. However, they also introduce certain security and management challenges. Here are some policies that an enterprise-level organization should consider when implementing wildcard certificates in their environment:

  • Approval Process

    Establish a process for requesting, validating and approving wildcard certificate requests. Must use exception process to request wildcard certificates that means, requesting a wildcard certificate is not the standard practice or the default way of obtaining certificates within the organization; it has to follow an exception process such as approval of leadership (Directors, VP).

  • Identify Subdomains

    Identify all subdomains that the wildcard certificate will cover. Determine which subdomains must be secured and ensure they adhere to your organization’s naming conventions.

  • Certificate management policies

    Create a clear policy for the wildcard certificate issuance, renewal, and revocation in your “Certificate Policy (CP)” and “Certificate Practice Statement (CPS)”. Specify who is responsible for managing the certificates.

  • Subdomain Naming Conventions

    Establish clear naming conventions for subdomains that wildcard certificates will secure. This helps ensure consistency and clarity in certificate management.

  • Provide Accurate Information

    Ensure that all information provided during the certificate issuance process is accurate, up to date, and should include all endpoints intended for the certificate. This includes proper naming convention for the certificate (according to organizational preferences and requirements), contact information, organization details (if applicable), domain ownership information, and provide justification to request a certificate.

  • Key Management

    Implement strong key management practices, including the secure generation and storage of private keys associated with wildcard certificates. Regularly rotate keys and update certificate configurations including certificate templates and protocol compatibility to stay ahead of potential vulnerabilities.

  • Access Control

    Limit access to wildcard certificates and their private keys to authorized personnel only. Enforce strict access controls and authentication mechanisms to prevent unauthorized access.

  • Certificate Revocation Policy

    Define a clear process for revoking wildcard certificates in case they are compromised or no longer needed. Ensure that revoked certificates are promptly removed from all relevant systems.

  • Inventory and Documentation

    Maintain an up-to-date inventory of all wildcard certificates in use within the organization. Document certificate details, including expiration dates, associated subdomains, and responsible parties.

  • Secure Storage

    Store wildcard certificates and their private keys in a secure, offline, or hardware security module (HSM) protected environment. Encrypt and back up certificate data to prevent data loss.

  • Certificate Renewal process

    Establish a process for timely certificate renewal to avoid service disruptions due to expired certificates. Automate certificate renewal where possible to reduce manual errors.

  • Security Awareness and Training

    Educate employees about the importance of wildcard certificate security and the risks associated with mishandling them.

  • Regular Security Assessment

    Conduct regular security assessments and penetration testing to identify vulnerabilities related to wildcard certificates and their usage.

  • Compliance and Industry Standard

    Ensure that wildcard certificate management practices align with industry standards and regulations relevant to OU, such as PCI DSS or HIPAA.

  • Usage of Wildcard Certificate

    Usage of wildcard certificates should be avoided whenever possible. Create a comprehensive plan for gradually decreasing the usage of wildcard certificates when they come up for renewal.

Recommendation for Future Action

Below recommendation will be useful for the organization’s future action for wildcard certificates.

  • Interim Measure

    Minimize the individuals with access to wildcard certificates, ideally limiting it to fewer personnel. Implement strict controls over the handling of the private key and certificate, treating them with the utmost security. Avoid electronic transmission and HDD storage; instead, opt for secure physical storage methods like Hardware Signing Module (HSM) stored in a secure location. Ensure that each certificate installation is set as “non-exportable” to prevent potential leaks.

  • Medium Term

    Reduce use of wildcard certificates to the fewest number of systems possible. Use named certificates everywhere possible. This implies knowing where the wildcards are installed and planning for their replacement (if possible).

  • Long-Term Strategy

    Implement a requirement that all wildcard certificates must be generated or renewed exclusively through an automated process, with zero personnel interaction. It’s essential to note that this transition will necessitate significant planning and preparation.


Organization should implement strong certificate management policies and security practices (CP/CPS), regularly audit, and monitor the wildcard certificate usage, and consider alternatives such as using separate certificates for critical subdomains or implementing more granular security controls where necessary. While wildcard certificates can be a valuable tool, they should be used thoughtfully and securely within an organization’s overall security strategy.

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About the Author

Parnashree Saha is a cybersecurity professional passionate about data protection, including PKI, data encryption, key management, IAM, etc. She is currently working as an advisory services manager at Encryption Consulting LLC. With a specialized focus on public key infrastructure, data encryption, and key management, she is vital in guiding organizations toward robust encryption solutions tailored to customers' unique needs and challenges. Parnashree leverages her expertise to provide clients comprehensive advisory services to enhance their cybersecurity posture. From conducting thorough assessments to developing customized encryption strategies and implementing relevant data protection solutions, She is dedicated to assisting organizations in protecting their sensitive data from evolving threats.

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