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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
SC-089: Mass Revocation Planning - Aug 26, 2025

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
v1.0.12 - Ballot SMC014 - Oct 13, 2025

This ballot introduces requirements that a Certificate Issuer MUST deploy DNSSEC validation back to the IANA DNSSEC root trust anchor on all DNS queries associated with CAA record lookups performed by the Primary Network Perspective, effective March 15, 2026. The ballot is intended to maintain consistency in the S/MIME Baseline Requirements with the requirements of Ballot SC-085 which implemented identical requirements in the TLS Baseline Requirements. Note: SC-085 also introduced requirements in TLS Baseline Requirements for the use of DNSSEC in domain control validation. These requirements are automatically adopted in the S/MIME BR by the email domain control methods that include a normative reference to section 3.2.2.4 of the TLS Baseline Requirements. The draft also includes minor corrections to web links in the text. This ballot is proposed by Stephen Davidson (DigiCert) and endorsed by Client Wilson (Apple) and Ashish Dhiman (GlobalSign).

Network and Certificate System Security Requirements
Version 2.0.5 (Ballot NS-008) - Jul 9, 2025

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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).