openssl/openssl

Requesting ability for policyMappings extension to parse mappings from one issuer domain to multiple subject domains

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#31087 opened on May 5, 2026

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help wantedissue: feature requesttriaged: feature

Description

When building a certificate profile in openssl.cnf for a cross certificate, the policyMappings extension cannot process multiple mappings from one issuer policy to multiple subject policies.

In this case, the second occurrence of the issuer:subject mapping wins.

Example snippet from my profile:

policyMappings = @cross_cert_mappings

[ cross_cert_mappings ]
2.16.840.1.999.1 = 2.16.840.1.666.1
2.16.840.1.999.2 = 2.16.840.1.666.2
2.16.840.1.999.2 = 2.16.840.1.777.1
2.16.840.1.999.3 = 2.16.840.1.666.3

When signing the cert with openssl ca, i get this:

X509v3 Policy Mappings:
   2.16.840.1.999.1:2.16.840.1.666.1, 
   2.16.840.1.999.2:2.16.840.1.777.1, 
   2.16.840.1.999.3:2.16.840.1.666.3

So this (first) occurrence of the issuer:subject policy mapping ending in .2 policy is lost in the final certificate: 2.16.840.1.999.2:2.16.840.1.666.2

There is a workaround by manually creating the ASN.1 structure of the policyMappings extension and then adding it to the profile (sample python script attached to do this, i've also done similar with openssl asn1parse -genconf):

2.5.29.33 = DER:30503012060760864801876701060760864801851a013012060760864801876702060760864801851a0230120607608648018767020607608648018609013012060760864801876703060760864801851a03

Which correctly produces the following:

X509v3 Policy Mappings:
2.16.840.1.999.1:2.16.840.1.666.1,
2.16.840.1.999.2:2.16.840.1.666.2,
2.16.840.1.999.2:2.16.840.1.777.1,
2.16.840.1.999.3:2.16.840.1.666.3

But this is tedious and having the extension be able to parse multiple occurrences of one issuer policy to multiple subject policies would be very helpful.

Thanks!

openssl-create-policyMappings-manually.py

Contributor guide

Tech stack
c
Domain
security
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
X.509 policiesOpenSSL configurationC programmingASN.1 basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
The issue is in the policyMappings extension parsing in OpenSSL's configuration. The relevant code is likely in crypto/x509/v3 policies.c where the policy mappings are parsed from config. The current implementation overwrites duplicate issuer policies; it needs to be changed to accept multiple mappings per issuer. The attached Python script demonstrates the correct ASN.1 structure, which can guide the implementation. Tests should be added to verify multiple mappings.