Re: TLS "trusted-dn" Question

I have opened a PR: https://github.com/syslog-ng/syslog-ng/pull/4412 :)

On Mon, Apr 3, 2023 at 2:36 PM Attila Szakács <[email protected]>
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 <[email protected]> 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). 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 <[email protected]> *On Behalf Of *Attila
>> Szakács
>> *Sent:* Thursday, March 30, 2023 3:12 AM
>> *To:* Syslog-ng users' and developers' mailing list <
>> [email protected]>
>> *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%7C4d2481e9962047dc420d08db31073b8e%7Cec65e18eede24cedbdab49355e3f602d%7C0%7C0%7C638157679363439549%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=wL9mYnHT0wDAWeUPj1DCRdF1DcwQUpguUech2vhKb7s%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%7C4d2481e9962047dc420d08db31073b8e%7Cec65e18eede24cedbdab49355e3f602d%7C0%7C0%7C638157679363439549%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=v1Hbhcgm4Bf2zw0AYF6%2F177xXLXxjkU5HhwLPCBfDS0%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 <[email protected]>
>> 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%7C4d2481e9962047dc420d08db31073b8e%7Cec65e18eede24cedbdab49355e3f602d%7C0%7C0%7C638157679363439549%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=X5NIUWuYD5F4GQ6WbnW%2F5HMrjJFkeg%2Fh4ma9xUMdN8w%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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>>

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