CA/Browser Forum
Home » Working Groups » Server Cert WG » Guidance on IP Addresses in Certificates

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
SC099: Improve Recording of Validation Methods - May 19, 2026

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
v1.0.14 - Ballot SMC016 - May 5, 2026

This ballot maintains consistency between the S/MIME Baseline Requirements and the TLS Baseline Requirements with changes introduced by Ballots SC096 and SC097. Specifically, this ballot: Creates a carve-out of the logging requirements for DNSSEC specifically, stating these are not in scope. For audit purposes, change management logging is able to confirm if the appropriate controls are in effect or not. Sunsets all remaining use of SHA-1 signatures in Certificates and CRLs. It is noted that most uses of SHA-1 signatures are already deprecated by SC097. With this ballot, all unexpired Subordinate CA Certificates issuing S/MIME containing the SHA-1 signature algorithm must be revoked. This proposal does not prohibit the use of SHA-1 to generate issuerKeyHash or issuerNameHash values as currently required by RFC 5019. Includes minor formatting corrections.

Unable to retrieve latest release information from the netsec repository.
Edit this page
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).