TLS/SSL (im_ssl)
The im_ssl module uses the OpenSSL library to provide an SSL/TLS transport. It behaves like the im_tcp module, except that an SSL handshake is performed at connection time and the data is sent 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 im_ssl module provides a secure log message transport.
Configuration
The im_ssl module accepts the following directives in addition to the common module directives.
TLS/SSL directives
The following directives are for configuring secure data transfer via TLS/SSL.
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 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 client. 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 client’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 client. A remote client’s self-signed certificate (which is not signed by a CA) can be trusted by specifying the remote client certificate itself. In the 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 specifies the thumbprint of the certificate authority (CA) certificate that will be used to verify the certificate presented by the remote client. 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 Agent. This directive is only supported on Windows and is mutually exclusive with the CADir and CAFile directives. |
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This specifies the path of the certificate file that will be presented to the remote client 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 specifies the thumbprint of the certificate that will be presented to the remote client 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 boolean value specifies that the remote client must present a certificate.
If set to |
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This optional boolean directive, when set 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
The module accepts connections on the IP address or hostname and port defined here.
The default address is To listen on multiple addresses or ports in a single module instance, this directive can be repeated multiple times. Both IPv4 and IPv6 addresses are supported. If a DNS name is used, the number of addresses or cnames should be kept below 16 to avoid potential issues caused by DNS response size limits.
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This optional directive can be used to allow IP addresses and/or networks to connect. The directive can be set multiple times to add different IPs or networks to allow. This directive is only active when the ListenAddr directive is present. In the absence of this directive, the BlockIP directive is considered. If both AllowIP and BlockIP are absent, then hosts are not restricted from connecting to a listening module. The following formats may be used for the AllowIP directive:
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This optional directive can be used to deny IP addresses and/or networks to connect. The directive can be set multiple times to add different IPs or networks to deny. This directive is only active when the ListenAddr directive is present. In the absence of this directive, the AllowIP directive is considered. If both AllowIP and BlockIP are absent, then hosts are not restricted from connecting to a listening module. The following formats may be used for the BlockIP directive:
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This optional boolean directive specifies whether the module instance should exclusively bind to the specified port.
The default value is
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This optional boolean directive determines whether the module instance should forcibly bind to a port already in use.
The default value is |
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This optional boolean directive specifies whether multiple im_ssl module instances can listen on the same port.
When you enable this directive, multiple instances run in a separate thread, allowing NXLog Agent to process incoming logs simultaneously.
See the examples below.
The default value is
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Examples
This configuration accepts secured log messages in the NXLog Agent binary format and writes them to a file.
<Input ssl>
Module im_ssl
ListenAddr localhost:23456
CAFile %CERTDIR%/ca.pem
CertFile %CERTDIR%/client-cert.pem
CertKeyFile %CERTDIR%/client-key.pem
KeyPass secret
InputType Binary
</Input>
<Output file>
Module om_file
File "tmp/output"
</Output>
<Route ssl_to_file>
Path ssl => file
</Route>