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Guidance on IP Addresses in Certificates

Introduction and problem description

The CA/B Forum Baseline Requirements are aligned with RFC 5280. According to the Baseline Requirements, if an X.509 v.3 certificate contains an IP Address, it MUST be included in the Subject Alternative Name (SAN) extension as an iPAddress name form (not dNSName). Multiple IP addresses can be included in the same certificate.

Browser certificate validation implementations should be able to follow these guidelines. However, there are some legacy implementations (mainly on Windows Operating Systems prior to version 10) that cannot properly handle the iPAddress name form in certificate SAN extensions.

Recommended Solution

These legacy implementations are capable of properly validating an IP address if it is included in the deprecated (discouraged but not prohibited) commonName field of the X.509 v.3 certificate Subject. This means that certificates that contain a SAN extension with an iPAddress that is ALSO included in the commonName, should be verified correctly by latest and legacy validation implementations.

Until legacy implementations fix their code to properly handle the iPAddress values from the SAN extension, this “solution” is consistent with the Baseline Requirements and RFC5280. The only limitation for this recommendation is that it is not possible to include multiple IP addresses in the common name of a single certificate.

CAs are required to use this practice which is consistent with the current standards and stop including IP addresses in the dNSName form of SAN extensions.

Server Cert WG
Latest releases
Server Certificate Requirements
BRs/2.1.2 SC-080 V3: Sunset the use of WHOIS to identify Domain Contacts and relying DCV Methods - Dec 16, 2024

Ballot SC-080 V3: “Sunset the use of WHOIS to identify Domain Contact… (https://github.com/cabforum/servercert/pull/560) Ballot SC-080 V3: “Sunset the use of WHOIS to identify Domain Contacts and relying DCV Methods” (https://github.com/cabforum/servercert/pull/555)

Code Signing Requirements
v3.8 - Aug 5, 2024

What’s Changed CSC-25: Import EV Guidelines to CS Baseline Requirements by @dzacharo in https://github.com/cabforum/code-signing/pull/38 Full Changelog: https://github.com/cabforum/code-signing/compare/v3.7...v3.8

S/MIME Requirements
v1.0.8 - Ballot SMC010 - Dec 23, 2024

This ballot adopts Multi-Perspective Issuance Corroboration (MPIC) for CAs when conducting Email Domain Control Validation (DCV) and Certification Authority Authorization (CAA) checks for S/MIME Certificates. The Ballot adopts the MPIC implementation consistent with the TLS Baseline Requirements. Acknowledging that some S/MIME CAs with no TLS operations may require additional time to deploy MPIC, the Ballot has a Compliance Date of May 15, 2025. Following that date the implementation timeline described in TLS BR section 3.2.2.9 applies. This ballot is proposed by Stephen Davidson (DigiCert) and endorsed by Ashish Dhiman (GlobalSign) and Nicolas Lidzborski (Google).

Network and Certificate System Security Requirements
v2.0 - Ballot NS-003 - Jun 26, 2024

Ballot NS-003: Restructure the NCSSRs in https://github.com/cabforum/netsec/pull/35

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The Certification Authority Browser Forum (CA/Browser Forum) is a voluntary gathering of Certificate Issuers and suppliers of Internet browser software and other applications that use certificates (Certificate Consumers).