TLS/SSL (om_ssl)
The om_ssl module uses the OpenSSL library to provide an SSL/TLS transport. It behaves like the om_tcp module, except that an SSL handshake is performed at connection time and the data is received over a secure channel. Log messages transferred over plain TCP can be eavesdropped or even altered with a man-in-the-middle attack, while the om_ssl module provides a secure log message transport.
Configuration
The om_ssl module accepts the following directives in addition to the common module directives. The Host directive is required.
Required directives
The following directives are required for the module to start.
The module connects to the IP address or hostname defined in this directive. If additional hosts are specified on new lines, the module works in a failover configuration. If a destination becomes unavailable, the module automatically fails over to the next one. If the last destination becomes unavailable, the module fails over to the first destination. The port number can be defined by appending it at the end of the hostname or IP address using a colon as a separator ( |
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The module connects to the port number on the destination host defined in this directive. This configuration is only used for any destination that does not have a port number specified in the Host directive. If no port is configured for a destination in either directive, the default port is used, which is port 514.
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TLS/SSL directives
This boolean directive specifies whether the connection should be allowed with an expired certificate.
If set to |
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This boolean directive specifies whether the certificate
FQDN should be validated against the server hostname or not.
If set to |
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This boolean directive specifies that the connection should be allowed regardless of the certificate verification results.
If set to |
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This directive specifies a path to a directory containing certificate authority (CA) certificates. These certificates will be used to verify the certificate presented by the remote server. The certificate files must be named using the OpenSSL hashed format, i.e. the hash of the certificate followed by .0, .1 etc. To find the hash of a certificate using OpenSSL: For example, if the certificate hash is A remote server’s self-signed certificate (which is not signed by a CA) can also be trusted by including a copy of the certificate in this directory. The default operating system root certificate store will be used if this directive is not specified.
Unix-like operating systems commonly store root certificates in |
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This specifies the path of the certificate authority (CA) certificate that will be used to verify the certificate presented by the remote server. A remote server’s self-signed certificate (which is not signed by a CA) can be trusted by specifying the remote server certificate itself. In case of certificates signed by an intermediate CA, the certificate specified must contain the complete certificate chain (certificate bundle). |
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This optional directive, supported only on Windows, defines a pattern for locating a suitable CA (Certificate Authority) certificate and its thumbprint in the native Windows Certificate Storage.
The pattern must follow PCRE2 rules and use the format Configuration examples: or A normal log output example would look like as follows: |
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This optional directive specifies the thumbprint of the certificate authority (CA) certificate that will be used to verify the certificate presented by the remote server. The hexadecimal fingerprint string can be copied from Windows Certificate Manager (certmgr.msc). Whitespaces are automatically removed. The certificate must be added to a Windows certificate store that is accessible by NXLog. This directive is only supported on Windows and is mutually exclusive with the CADir, CAFile and CAPattern directives. |
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This specifies the path of the certificate file that will be presented to the remote server during the SSL handshake. |
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This specifies the path of the private key file that was used to generate the certificate specified by the CertFile directive. This is used for the SSL handshake. |
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This optional directive, supported only on Windows, defines a pattern for identifying a corresponding certificate and its thumbprint within the native Windows Certificate Storage.
The pattern must follow PCRE2 rules and use the format Configuration examples: or A normal log output example would look like as follows: |
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This optional directive specifies the thumbprint of the certificate that will be presented to the remote server during the SSL handshake.
The hexadecimal fingerprint string can be copied from Windows Certificate Manager (certmgr.msc).
Whitespaces are automatically removed.
The certificate must be imported to the This directive is only supported on Windows and is mutually exclusive with the CertFile and CertKeyFile directives.
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This directive specifies a path to a directory containing certificate revocation list (CRL) files. These CRL files will be used to check for certificates that were revoked and should no longer be accepted. The files must be named using the OpenSSL hashed format, i.e. the hash of the issuer followed by .r0, .r1 etc. To find the hash of the issuer of a CRL file using OpenSSL: For example if the hash is |
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This specifies the path of the certificate revocation list (CRL) which will be used to check for certificates that have been revoked and should no longer be accepted. Example to generate a CRL file using OpenSSL: |
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This optional directive specifies a file with dh-parameters for Diffie-Hellman key exchange. These parameters can be generated with dhparam(1ssl). If this directive is not specified, default parameters will be used. See the OpenSSL Wiki for further details. |
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This directive specifies the passphrase of the private key specified by the CertKeyFile directive. A passphrase is required when the private key is encrypted. Example to generate a private key with Triple DES encryption using OpenSSL: This directive is not needed for passwordless private keys. |
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This optional boolean directive, when set to |
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This optional directive enables the logging of the TLS protocol version and cipher suite upon a successful SSL/TLS handshake.
Setting this directive to |
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This optional directive can be used to set the permitted cipher list for TLSv1.2 and below, overriding the default.
Use the format described in the ciphers(1ssl) man page.
For example specify
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This optional directive can be used to set the permitted cipher list for TLSv1.3. Use the same format as in the SSLCipher directive. Refer to the OpenSSL documentation for a list of valid TLS v1.3 cipher suites. The default value is:
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This boolean directive allows you to enable data compression when sending data over the network.
The compression mechanism is based on the zlib compression library.
If the directive is not specified, it defaults to
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This directive can be used to set the allowed SSL/TLS protocol(s). It takes a comma-separated list of values which can be any of the following: |
Optional directives
This optional directive specifies the local port number of the connection. If this is not specified, a random high port number will be used, which is not always ideal in firewalled network environments.
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See the OutputType directive in the list of common module directives. The default is LineBased_LF. |
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This optional directive sets the reconnect interval in seconds. If it is set, the module attempts to reconnect in every defined second. If it is not set, the reconnect interval will start at 1 second and doubles with every attempt. If the duration of the successful connection is greater than the current reconnect interval, then the reconnect interval will be reset to 1 sec.
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This optional directive specifies the hostname used for Server Name Indication (SNI). If not specified, it defaults to the hostname in the Host directive. |
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This boolean directive is used to turn off the network optimization performed by Nagle’s algorithm. Nagle’s algorithm is a network optimization tweak that tries to reduce the number of small packets sent out to the network, by merging them into bigger frames, and by not sending them to the other side of the session before receiving the ACK. If this directive is unset, the TCP_NODELAY socket option will not be set. |
Procedures
The following procedures are exported by om_ssl.
reconnect();-
Force a reconnection. This can be used from a Schedule block to periodically reconnect to the server.
The reconnect() procedure must be used with caution. If configured, it can attempt to reconnect after every event sent, potentially overloading the destination system.
Examples
Pre-v5 syntax examples are included, they will become invalid with NXLog Enterprise Edition 6.0.
This configuration reads log messages from socket and sends them in the NXLog binary format to another NXLog agent.
<Input uds>
Module im_uds
UDS tmp/socket
</Input>
<Output ssl>
Module om_ssl
Host example.com:23456
CAFile %CERTDIR%/ca.pem
CertFile %CERTDIR%/client-cert.pem
CertKeyFile %CERTDIR%/client-key.pem
KeyPass secret
AllowUntrusted TRUE
OutputType Binary
</Output>
# Using the syntax prior to NXLog Enterprise Edition 5,
# where the port is defined in a separate directive.
#<Output ssl>
# Module om_ssl
# Host example.com
# Port 23456
# CAFile %CERTDIR%/ca.pem
# CertFile %CERTDIR%/client-cert.pem
# CertKeyFile %CERTDIR%/client-key.pem
# KeyPass secret
# AllowUntrusted TRUE
# OutputType Binary
#</Output>This configuration sends logs to another NXLog agent in a failover configuration (multiple Hosts defined).
<Output ssl>
Module om_ssl
Host 192.168.1.2:23456
Host 192.168.1.3:23456
Host example.com:1514
CAFile %CERTDIR%/ca.pem
</Output>
