[syslog-ng] TLS "trusted-dn" Question

David Hauck davidh at netacquire.com
Mon Apr 3 18:37:01 UTC 2023 

Hi Attila,

Great, thx for working on this!

I think if would be best if we got back to this after the merge to main is complete and a new release is generated. I’m running this on a custom distro so I will need to work with the distro vendor to get this integrated before I can get a runtime image that will work on my test systems. It’s also feasible for me to run a common distro (Ubuntu or Fedora derivative) as a VM for testing, but this also will take some setting up. Let me know if you’re really stuck getting this tested and then I can try to rig something up here.

Thanks again,
-David

PS: Ultimately moving to the current release (with this feature added) will involve more work for us to validate, given the existing v3.31.2 runtimes. This includes (potentially) work to upgrade the configuration. Can you say anything about what might be involved in upgrading a (fairly generic, but fairly intricate) v3.31.2 configuration to v4.x.x?

From: syslog-ng <syslog-ng-bounces at lists.balabit.hu> On Behalf Of Attila Szakács
Sent: Monday, April 03, 2023 9:04 AM
To: Syslog-ng users' and developers' mailing list <syslog-ng at lists.balabit.hu>
Subject: Re: [syslog-ng] TLS "trusted-dn" Question

I have opened a PR: https://github.com/syslog-ng/syslog-ng/pull/4412<https://usg02.safelinks.protection.office365.us/?url=https%3A%2F%2Fgithub.com%2Fsyslog-ng%2Fsyslog-ng%2Fpull%2F4412&data=05%7C01%7Cdavidh%40netacquire.com%7C7f3b7f7db2cf411828e508db345d1aba%7Cec65e18eede24cedbdab49355e3f602d%7C0%7C0%7C638161346727644149%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=3tI6DxNYsGaIQ%2F8fnGzj%2FHbAGy3GUQRIAqNFmgdtS9Y%3D&reserved=0> :)

On Mon, Apr 3, 2023 at 2:36 PM Attila Szakács <attila.szakacs at axoflow.com<mailto:attila.szakacs at axoflow.com>> wrote:
Thanks! I will try to implement it this week, or if I won't have the time for it, I will create a feature request for it.

In the meantime, I would like to ask: will there be any way you can try out the new feature before a stable release? I can provide you deb or rpm packages or a container image manually, or when we merge it to master, it will be available in our nightly APT repo and nightly docker image. I can provide you a patch, if you are building locally, but I am afraid that the change won't trivially apply to 3.31, as there have been modifications around TLS since then. Does any of this work for you?

Cheers,
Attila

On Thu, Mar 30, 2023 at 5:32 PM David Hauck <davidh at netacquire.com<mailto:davidh at netacquire.com>> wrote:
Hi Attila,

The trusted-dn() option is used for an additional verification step to reject clients/servers

Ah, OK, yes, I think I misread (or misinterpreted) this. I get how this is used now, thx.

Could you kindly confirm that this is what you are looking for?

Yes, exactly. This is similar to what (for e.g.) the SSLCACertificate{File|Path} mod_ssl directives are used for with the Apache HTTP Server and its HTTPS operation (see https://httpd.apache.org/docs/2.4/mod/mod_ssl.html<https://usg02.safelinks.protection.office365.us/?url=https%3A%2F%2Fhttpd.apache.org%2Fdocs%2F2.4%2Fmod%2Fmod_ssl.html&data=05%7C01%7Cdavidh%40netacquire.com%7C7f3b7f7db2cf411828e508db345d1aba%7Cec65e18eede24cedbdab49355e3f602d%7C0%7C0%7C638161346727644149%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Y%2BGb1rgUzAQcoNoPTZYkrbGr%2BSqpfBD6ZE6XmETALNE%3D&reserved=0>). Without this connecting clients aren’t given any hints that can help them provide a proper client certificate (when they otherwise have many to choose from, each possibly signed by different CAs).

Thanks,
-David

From: syslog-ng <syslog-ng-bounces at lists.balabit.hu<mailto:syslog-ng-bounces at lists.balabit.hu>> On Behalf Of Attila Szakács
Sent: Thursday, March 30, 2023 3:12 AM
To: Syslog-ng users' and developers' mailing list <syslog-ng at lists.balabit.hu<mailto:syslog-ng at lists.balabit.hu>>
Subject: Re: [syslog-ng] TLS "trusted-dn" Question

Hi David,

The trusted-dn() option is used for an additional verification step to reject clients/servers, which provide a cert having such a subject field that does not match with any of the patterns set in trusted-dn().

Unfortunately, I think that the first sentence in the documentation is a bit misleading:
Description: To accept connections only from hosts using certain certificates signed by the trusted CAs, list the distinguished names of the accepted certificates in this parameter. For example, using trusted-dn("*, O=Example Inc, ST=Some-State, C=*") will accept only certificates issued for the Example Inc organization in Some-State state.

If I understand correctly, what you would like to achieve is defined in https://www.ietf.org/rfc/rfc5246.txt<https://usg02.safelinks.protection.office365.us/?url=https%3A%2F%2Fwww.ietf.org%2Frfc%2Frfc5246.txt&data=05%7C01%7Cdavidh%40netacquire.com%7C7f3b7f7db2cf411828e508db345d1aba%7Cec65e18eede24cedbdab49355e3f602d%7C0%7C0%7C638161346727800365%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Y%2BrLItCfeBYP%2FOGdRzWHznnMi80f9hWMSQ8%2FJNY1vTE%3D&reserved=0> -> 7.4.4. Certificate Request:

   certificate_authorities

      A list of the distinguished names [X501] of acceptable

      certificate_authorities, represented in DER-encoded format.  These

      distinguished names may specify a desired distinguished name for a

      root CA or for a subordinate CA; thus, this message can be used to

      describe known roots as well as a desired authorization space.  If

      the certificate_authorities list is empty, then the client MAY

      send any certificate of the appropriate ClientCertificateType,

      unless there is some external arrangement to the contrary.



This is not implemented in syslog-ng, yet, but it could be done easily with SSL_set_client_CA_list()<https://usg02.safelinks.protection.office365.us/?url=https%3A%2F%2Fwww.openssl.org%2Fdocs%2Fman3.0%2Fman3%2FSSL_get0_CA_list.html&data=05%7C01%7Cdavidh%40netacquire.com%7C7f3b7f7db2cf411828e508db345d1aba%7Cec65e18eede24cedbdab49355e3f602d%7C0%7C0%7C638161346727800365%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Pk7pU%2Ft01LoCJbs8hS6Vt08tsCD5Ex%2Bgu5C2EceHrmc%3D&reserved=0>:

SSL_set_client_CA_list() sets the list of CAs sent to the client when requesting a client certificate for the chosen ssl, overriding the setting valid for ssl's SSL_CTX object.
Could you kindly confirm that this is what you are looking for?

Cheers,
Attila

On Wed, Mar 29, 2023 at 8:42 PM David Hauck <davidh at netacquire.com<mailto:davidh at netacquire.com>> wrote:
Hi,

I'm currently using syslog-ng OSE v3.31.2 and trying to get a TLS configured endpoint to use the 'trusted-dn()' TLS option. I'm having trouble getting syslog-ng to return these DN specifiers in the Certificate Request option during the TLS negotiation so that clients can properly condition their supplied client certificates.

I invariably see the following TLS negotiations (empty DNs list) in my Wireshark captures (as returned by the syslog-ng server):

TLSv1.2 Record Layer: Handshake Protocol: Certificate Request
    Content Type: Handshake (22)
    Version: TLS 1.2 (0x0303)
    Length: 58
    Handshake Protocol: Certificate Request
        Handshake Type: Certificate Request (13)
        Length: 54
        Certificate types count: 3
        Certificate types (3 types)
        Signature Hash Algorithms Length: 46
        Signature Hash Algorithms (23 algorithms)
        Distinguished Names Length: 0                          <----- always '0'

In these cases my clients choose random client certificates that can't be refined to certificates signed by those expected (via the 'trusted-dn()' values) by the server and the connection is immediately closed.

Here's the syslog-ng.conf entry for these sources:

source s_515_tls {
   network( transport(tls) port(515) ip-protocol(6)
      tls(ca-dir("/etc/ssl/certs") key-file("/root/naservers.key") cert-file("/root/naservers.cer")
         peer-verify(required-trusted) trusted-dn("CN=*.netacquire.com<https://usg02.safelinks.protection.office365.us/?url=http%3A%2F%2Fnetacquire.com%2F&data=05%7C01%7Cdavidh%40netacquire.com%7C7f3b7f7db2cf411828e508db345d1aba%7Cec65e18eede24cedbdab49355e3f602d%7C0%7C0%7C638161346727800365%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=w2ZnIVpwm0j%2FK6aUUMcwPL%2FIy%2FI5efo5wnhc0AfhvJw%3D&reserved=0>")) );
};

I've tried several variants of the 'trusted-dn()' values, including other wildcards for country, state, etc. I always see a DNs list of zero size in the TLS Certificate Request option returned by the server. As expected switching to 'peer-verify(required-untrusted)' results in successful negotiation (with expected server-side errors indicating problems associated with the client certificates) and subsequent successful client/server logging.

I figure I must be missing something obvious ;). Any ideas?

Here's my syslog-ng version info:

[logdest:~]# syslog-ng --version
syslog-ng 3 (3.31.2)
Config version: 3.29
Installer-Version: 3.31.2
Revision:
Compile-Date: Nov  9 2021 12:52:59
Module-Directory: /usr/lib/syslog-ng
Module-Path: /usr/lib/syslog-ng
Include-Path: /usr/share/syslog-ng/include
Available-Modules: tfgetent,mod-python,cryptofuncs,hook-commands,kvformat,cef,afuser,linux-kmsg-format,map-value-pairs,system-source,azure-auth-header,csvparser,affile,afprog,secure-logging,http,examples,timestamp,afsocket,confgen,stardate,dbparser,xml,disk-buffer,appmodel,afsnmp,add-contextual-data,afstomp,graphite,json-plugin,basicfuncs,syslogformat,pseudofile,tags-parser
Enable-Debug: off
Enable-GProf: off
Enable-Memtrace: off
Enable-IPv6: on
Enable-Spoof-Source: off
Enable-TCP-Wrapper: on
Enable-Linux-Caps: on
Enable-Systemd: off

Thanks,
-David
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