NSA Issues Warning About Wildcard TLS Certificates In Relation To An Exploit Called ALPACA

The U.S. National Security Agency (NSA) recently put out a warning for organizations to avoid the dangers of Wildcard TLS certificates in relation to an exploit called the ALPACA.  According to the statement:

A new style of web application exploitation, dubbed “ALPACA,” increases the risk from using broadly scoped wildcard certificates to verify server identities during the Transport Layer Security (TLS) handshake. Application Layer Protocols Allowing Cross-Protocol Attack (ALPACA) is a technique used to exploit hardened web applications through non- HTTP (Hypertext Transfer Protocol) services secured using the same or a similar TLS certificate. This Cybersecurity Information Sheet details the risks from wildcard certificates and ALPACA, and provides mitigations for both.

Administrators should assess their environments to ensure that their certificate usage, especially the use of wildcard certificates, does not create unmitigated risks, and in particular, that their organizations’ web servers are not vulnerable to ALPACA techniques.

Chris Hickman, chief security officer at Keyfactor had this to say:

“Using wildcard certs is like issuing a driver’s license to an address rather than a person.  It assumes everyone at the address meets the same criteria of identification.

A single certificate should not be used to represent multiple machines or endpoints. While having unique certs for each TLS/SSL endpoint allows for the orderly and unique identification of each asset, it requires comprehensive and automated management of the certificates in order to scale.

Wildcard certificates can be very helpful for organizations seeking to secure a number of subdomains, but their use creates significant security risks since the same private key is used across dispersed systems, increasing the risk of an organization-wide compromise.

Whether you are using wildcard certificates or not, ensure that you have visibility into every certificate your organization possesses and establish processes to renew or replace them. Except for limiting the use of wildcard certificates in your organization, here is what you must do to ensure an effective certificate lifecycle management:

  • Keep an accurate and up-to-date inventory of certificates in your environment, documenting key length, hash algorithm, expiry, locations, and the certificate owner.
  • Ensure that private keys are stored and protected according to industry’s best practices (i.e., using a certified HSM).
  • Automate certificate renewal, revocation, and provisioning processes to prevent unexpected expirations and outages.”

I am personally evaluating both my email servers to see if they are affected by this as I use wildcard certificates to secure them. Even if I am not affected, I will be re-evaluating if I should be using wildcard certificates going forward.

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