Re: certificate validation fails for trusted self-signed server certificate

That was it, the certificate was different!
I took a snapshot of the certificate a few days ago and it is still valid 
(not expired), but yesterday they replaced it with a fresh one.

Thank you for the help, much appreciated!

On Thursday, August 7, 2025 at 5:25:54 AM UTC+3 Viktor Dukhovni wrote:

> On Wed, Aug 06, 2025 at 09:05:33AM -0700, Cosmin Banu wrote:
>
> > I have encountered a scenario with unexpected behavior when trying to 
> > connect an SSL client (custom client application) to a server that is 
> > configured with a self-signed server certificate (it's not marked as CA, 
> > it's a leaf certificate) - more specifically, the server I'm testing 
> > against is:
> > https://self-signed.badssl.com/
> > 
> > I've configured the client by loading the server's certificate in an 
> > X509_STORE and then set that store on the SSL_CTX and I've set the 
> verify 
> > mode to SSL_VERIFY_PEER.
> > 
> > The error I'm getting is X509_V_ERR_DEPTH_ZERO_SELF_SIGNED_CERT (error
> > code 18: "self-signed certificate"). The documentation for this error
> > suggests even more that this should not happen, since the certificate
> > was loaded into the store:
> > 
> https://github.com/openssl/openssl/blob/openssl-3.5/doc/man3/X509_STORE_CTX_get_error.pod?plain=1#L193
> > "The passed certificate is self-signed and the same certificate cannot
> > be found in the list of trusted certificates."
>
> It is perhaps the case that the server certificate loaded into the trust
> store is not completely identical with that presented over the wire,
> perhaps an older or different certificate with the same subject name is
> used on either end.
>
> > Is there something I'm missing? Some other configuration option? Or is 
> this 
> > the expected behavior?
>
> This works for me (with either the stock OpenSSL 3.2 from Fedora, or
> OpenSSL 3.5 as below):
>
> $ PATH=/opt/openssl/3.5/bin:$PATH
> $ rm /tmp/ck.pem
> $ openssl req -nodes -new -newkey ed25519 -keyout /dev/stdout \
> -x509 -days 30 -subj / \
> -addext "basicConstraints = critical,CA:false" \
> -addext "subjectKeyIdentifier = none" >> /tmp/ck.pem
>
> $ openssl s_server -cert /tmp/ck.pem -accept 127.0.0.1:12345 -quiet 
> -no_ign_eof &
>
> $ sleep 1 | openssl s_client -CAfile /tmp/ck.pem -connect 127.0.0.1:12345 
> -quiet -no_ign_eof -showcerts
> Connecting to 127.0.0.1
> Can't use SSL_get_servername
> depth=0
> verify return:1
> DONE
>
> $ openssl x509 -in /tmp/ck.pem -noout -text \
> -certopt 
> no_header,no_version,no_serial,no_signame,no_issuer,no_validity,no_subject,no_pubkey,no_sigdump
> X509v3 extensions:
> X509v3 Authority Key Identifier:
> 77:E1:C8:B6:23:4A:6C:5B:DE:7F:32:25:16:3C:64:3B:78:32:14:13
> X509v3 Basic Constraints: critical
> CA:FALSE
>
> The CA bit can be either "TRUE" or "FALSE", the SKID either present or
> absent, all the combinations work, provided the exact certificate
> presented by the server appears in the trust store.
>
> -- 
> Viktor. 🇺🇦 Слава Україні!
>

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