imdtls: Input Module for DTLS Protocol over UDP¶

Module Name:	imdtls
Author:	Andre Lorbach <alorbach@adiscon.com>
Available since:	v8.2402.0

Purpose¶

The imdtls module for rsyslog is designed to securely transport syslog messages over the network using the Datagram Transport Layer Security (DTLS) protocol. This module leverages the robustness and security features of OpenSSL to provide an encrypted transport mechanism for syslog messages via UDP.

DTLS, being an adaptation of TLS for datagram-based protocols, offers integrity, authenticity, and confidentiality for messages in transit. The imdtls module is particularly useful in environments where secure transmission of log data is crucial, such as in compliance-driven industries or when transmitting across untrusted networks.

By operating over UDP, imdtls offers the benefits of lower latency and reduced protocol overhead compared to TCP-based transport, making it well-suited for high-throughput logging scenarios or in networks where connection-oriented protocols may face challenges.

Requirements¶

To receive messages by DTLS you will need to fulfill the following requirements:

OpenSSL 1.0.2 or Higher

Configuration Parameters¶

Note

Parameter names are case-insensitive.

Action Parameters¶

address¶

type	default	mandatory	`obsolete legacy` directive
word	none	no	none

Specifies the IP address on where the imdtls module will listen for incoming syslog messages. By default the module will listen on all available network connections.

port¶

type	default	mandatory	`obsolete legacy` directive
word	4433	yes	none

Specifies the UDP port to which the imdtls module will bind and listen for incoming connections. The default port number for DTLS is 4433.

timeout¶

type	default	mandatory	`obsolete legacy` directive
word	1800	no	none

Specifies the DTLS session timeout. As DTLS runs on transportless UDP protocol, there are no automatic detections of a session timeout. The input will close the DTLS session if no data is received from the client for the configured timeout period. The default is 1800 seconds which is equal to 30 minutes.

name¶

type	default	mandatory	`obsolete legacy` directive	Available since
word	none	no	none

Unique name to the input module instance. This is useful for identifying the source of messages when multiple input modules are used.

ruleset¶

type	default	mandatory	`obsolete legacy` directive
word	none	no	none

Determines the ruleset to which the imdtls input will be bound to. This can be overridden at the instance level.

tls.AuthMode¶

type	default	mandatory	`obsolete legacy` directive
string	none	no	none

Sets the mode used for mutual authentication.

Supported values are either “fingerprint“, “name” or “certvalid“.

Fingerprint: Authentication based on certificate fingerprint. Name: Authentication based on the subjectAltName and, as a fallback, the subject common name. Certvalid: Requires a valid certificate for authentication. Certanon: Anything else will allow anonymous authentication (no client certificate).

tls.cacert¶

type	default	mandatory	`obsolete legacy` directive
string	none	no	none

The CA certificate that is being used to verify the client certificates. Has to be configured if tls.authmode is set to “fingerprint“, “name” or “certvalid“.

tls.mycert¶

type	default	mandatory	`obsolete legacy` directive
string	none	no	none

Specifies the certificate file used by imdtls. This certificate is presented to peers during the DTLS handshake.

tls.myprivkey¶

type	default	mandatory	`obsolete legacy` directive
string	none	no	none

The private key file corresponding to tls.mycert. This key is used for the cryptographic operations in the DTLS handshake.

tls.tlscfgcmd¶

type	default	mandatory	`obsolete legacy` directive
string	none	no	none

Used to pass additional OpenSSL configuration commands. This can be used to fine-tune the OpenSSL settings by passing configuration commands to the openssl libray. OpenSSL Version 1.0.2 or higher is required for this feature. A list of possible commands and their valid values can be found in the documentation: https://docs.openssl.org/1.0.2/man3/SSL_CONF_cmd/

The setting can be single or multiline, each configuration command is separated by linefeed (n). Command and value are separated by equal sign (=). Here are a few samples:

Example 1¶

This will allow all protocols except for SSLv2 and SSLv3:

tls.tlscfgcmd="Protocol=ALL,-SSLv2,-SSLv3"

Example 2¶

This will allow all protocols except for SSLv2, SSLv3 and TLSv1. It will also set the minimum protocol to TLSv1.2

tls.tlscfgcmd="Protocol=ALL,-SSLv2,-SSLv3,-TLSv1
MinProtocol=TLSv1.2"

TLS.PermittedPeer¶

type	default	mandatory	`obsolete legacy` directive
array	none	no	none

PermittedPeer places access restrictions on this listener. Only peers which have been listed in this parameter may connect. The certificate presented by the remote peer is used for it’s validation.

The peer parameter lists permitted certificate fingerprints. Note that it is an array parameter, so either a single or multiple fingerprints can be listed. When a non-permitted peer connects, the refusal is logged together with it’s fingerprint. So if the administrator knows this was a valid request, he can simply add the fingerprint by copy and paste from the logfile to rsyslog.conf.

To specify multiple fingerprints, just enclose them in braces like this:

tls.permittedPeer=["SHA1:...1", "SHA1:....2"]

To specify just a single peer, you can either specify the string directly or enclose it in braces. You may also use wildcards to match a larger number of permitted peers, e.g. *.example.com.

When using wildcards to match larger number of permitted peers, please know that the implementation is similar to Syslog RFC5425 which means: This wildcard matches any left-most DNS label in the server name. That is, the subject *.example.com matches the server names a.example.com and b.example.com, but does not match example.com or a.b.example.com.

Statistic Counter¶

This plugin maintains global statistics for imdtls that accumulate all action instances. The statistic origin is named “imdtls” with following counters:

submitted - This counter tracks the number of log messages that have been received by the current input instance.

These statistics counters are updated in real-time by the rsyslog output module as log data is processed, and they provide valuable information about the performance and operation of the input module.

For multiple actions using statistics callback, there will be one record for each action.

Examples¶

Example 1: Basic¶

The following sample does the following:

loads the imdtls module
outputs all logs to File

module(load="imdtls")
input(type="imdtls" port="4433")

action( type="omfile" file="/var/log/dtls.log")

Example 2: Require valid certificate¶

The following sample does the following:

loads the imdtls module
Validates the client certificate, requires same CA for client and server certificate
outputs all logs to File

module(load="imdtls")
input(type="imdtls"
      port="4433"
      tls.cacert="/etc/private/ca.pem"
      tls.mycert="/etc/private/cert.pem"
      tls.myprivkey="/etc/private/key.pem"
      tls.authmode="certvalid" )

action( type="omfile" file="/var/log/dtls.log")

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