AW: [EXTERNAL] Stricter pathlen checks in OpenSSL 1.1.1 compared to 1.0.2?.

Andrew Lynch andrew.lynch at
Fri Sep 16 08:32:27 UTC 2022

So is this a possible bug or a feature of OpenSSL 1.1.1?  (using 1.1.1n right now)

If I set up the content of CAfile or CApath so that E <- D <- C <- A is the only path that can be taken then the validation fails with

error 25 at 3 depth lookup: path length constraint exceeded

If I create the first root certificate (A) with pathlen:2 instead of pathlen:1 then validation succeeds

user1_cert.pem: OK
depth=0: C = DE, O = Test Org, CN = Test User (untrusted)           E
depth=1: C = DE, O = Test Org, CN = Test Sub-CA                              D
depth=2: C = DE, O = Test Org, CN = Test Root 2-CA                         C
depth=3: C = DE, O = Test Org, CN = Test Root 1-CA                         A

So it appears to me that OpenSSL 1.1.1n is definitely taking the pathlen constraint of certificate A into account.


Von: Erwann Abalea <erwann.abalea at>
Gesendet: Donnerstag, 15. September 2022 19:51
An: Andrew Lynch <andrew.lynch at>
Cc: openssl-users at
Betreff: Re: [EXTERNAL] Stricter pathlen checks in OpenSSL 1.1.1 compared to 1.0.2?.

Assuming that all self-signed certificates are trusted (here, A and B), then providing a CAfile with D+C+B+A to validate E, the different possible paths are:
 - E <- D <- B: this path is valid
 - E <- D <- C <- A: this path is valid

In the validation algorithm described in RFC5280 and X.509, the pathlenConstraints contained in the certificate of the Trust Anchor (here, A or B) is not taken into account. Therefore, the only ones that matter are the values set in C and D, and these values are coherent with both chains.

On Thu, Sep 15, 2022 at 7:34 PM Andrew Lynch via openssl-users <openssl-users at<mailto:openssl-users at>> wrote:

I would like to have my understanding of the following issue confirmed:

Given a two-level CA where the different generations of Root cross-sign each other, the verification of an end-entity certificate fails with OpenSSL 1.1.1 – “path length constraint exceeded”.  With OpenSSL 1.0.2 the same verify succeeds.

All Root CA certificates have Basic Constraints CA:TRUE, pathlen:1.  The Sub CA certificate has pathlen:0.

A) Issuer: CN=Root CA, serialNumber=1
   Subject: CN=Root CA, serialNumber=1

B) Issuer: CN=Root CA, serialNumber=2
   Subject: CN=Root CA, serialNumber=2

C) Issuer: CN=Root CA, serialNumber=1
   Subject: CN=Root CA, serialNumber=2

D) Issuer: CN=Root CA, serialNumber=2
   Subject: CN=Sub CA, serialNumber=2

E) Issuer: CN=Sub CA, serialNumber=2
   Subject: Some end entity

With a CAfile containing D, C, B, A in that order the verify of E fails.  If I remove the cross certificate C then the verify succeeds.

I believe OpenSSL 1.1.1 is building a chain of depth 3 (D – C – A) and so pathlen:1 of A is violated.  Without the cross certificate the chain is only depth 2 (D – B).

Is my understanding of the reason for this failure correct?
Why is OpenSSL 1.0.2 verifying successfully?  Does it not check the path length constraint or is it actually picking the depth 2 chain instead of the depth 3?


Erwann Abalea.
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