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.
|To examine the supported platforms, see the list of installer packages in the Available Modules chapter.|
The im_ssl module accepts the following directives in addition to the common module directives.
The module accepts connections on the IP address or hostname and port defined here. The default address is
localhostand the default port is 514. The port number can be defined by appending it at the end of the hostname or IP address using a colon as a separator (
host:port). IPv6 addresses must be enclosed in square brackets (
[host]:port). The port section of this directive and the Port directive are mutually exclusive. In case both are defined, the port number defined here takes precedence over a port defined in the Port directive. In case none of them is defined, the default port is used.
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.
|Formerly called Host, this directive is now ListenAddr. Host will become deprecated from NXLog EE 6.0 for incoming traffic.|
For client applications that don’t support IPv6, to avoid the behavior
described above the
Alternatively, the server-side system may be configured to prioritize IPv4
addresses for the hostname specified by the
For more information see the Microsoft documentation on Configuring IPv6 in Windows for advanced users.
This limitation will be addressed in a future release by making listening modules bind to all available IPv4/IPv6 addresses that a hostname resolves to.
The module listens for incoming connections on the port defined in this directive. The default is port 514.
|The Port directive will become deprecated from NXLog EE 6.0. After that, the port can only be defined in the ListenAddr directive.|
This optional directive may be used to specify a whitelist of IP addresses and/or networks that are allowed to connect. The directive can be specified more than once to add different IPs or networks to the whitelist. This directive is only active when the Listen or ListenAddr directives are present. In the absence of this directive, there is no restriction on the hosts which may connect to a listening module. The following formats may be used:
0.0.0.0/32(IPv4 network with subnet bits)
0.0.0.0/0.0.0.0(IPv4 network with subnet address)
aa::12/64(IPv6 network with subnet bits)
This boolean directive specifies whether the connection should be allowed with an expired certificate. If set to
TRUE, the remote client will be able to connect with an expired certificate. The default is
FALSE: the certificate must not be expired. This directive is only valid if RequireCert is set to
This boolean directive specifies that the connection should be allowed regardless of the certificate verification results. If set to
TRUE, the remote client will be able to connect with any unexpired certificate. The default value is
FALSE: the remote client must present a trusted certificate.
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:
$ openssl x509 -hash -noout -in ca.crt
For example if the certificate hash is
e2f14e4a, then the certificate filename should be
e2f14e4a.0. If there is another certificate with the same hash then it should be named
e2f14e4a.1and so on.
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.
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 case of certificates signed by an intermediate CA, the certificate specified must contain the complete certificate chain (certificate bundle).
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. This directive is only supported on Windows and is mutually exclusive with the CADir and CAFile directives.
This optional boolean directive, when set to
TRUE, enables the loading of all available Windows certificates into NXLog, for use during remote certificate verification. Any required certificates must be added to a Windows certificate store that NXLog can access. This directive is mutually exclusive with the CAThumbprint, CADir and CAFile directives.
This specifies the path of the certificate file that will be presented to the remote client during the SSL handshake.
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.
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
Local Computer\Personalcertificate store in PFX format for NXLog to find it. To create a PFX file from the certificate and private key using OpenSSL:
$ openssl pkcs12 -export -out server.pfx -inkey server.key -in server.pem
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:
$ openssl genrsa -des3 -out server.key 2048
This directive is not needed for passwordless private keys.
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:
$ openssl crl -hash -noout -in crl.pem
For example if the hash is
e2f14e4a, then the filename should be
e2f14e4a.r0. If there is another file with the same hash then it should be named
e2f14e4a.r1and so on.
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:
$ openssl ca -gencrl -out crl.pem
This boolean value specifies that the remote client must present a certificate. If set to
TRUEand a certificate is not presented during the SSL handshake, the connection will be refused. The default value is
TRUE: each connection must use a certificate.
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
RSA:!COMPLEMENTOFALLto include all ciphers with RSA authentication but leave out ciphers without encryption.
|If RSA or DSA ciphers with Diffie-Hellman key exchange are used, DHFile can be set for specifying custom dh-parameters.|
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:
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
FALSE: compression is disabled.
Some Linux packages (for example Debian) use the OpenSSL library provided by the OS and may not support the zlib compression mechanism. The module will emit a warning on startup if the compression support is missing. The generic deb/rpm packages are bundled with a zlib-enabled libssl library.
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:
TLSv1.3. By default, the
TLSv1.3protocols are allowed. Note that the OpenSSL library shipped by Linux distributions may not support
SSLv3, and these will not work even if enabled with this directive.
Pre-v5 syntax examples are included, they will become invalid with NXLog Enterprise Edition 6.0.
This configuration accepts secured log messages in the NXLog binary format and writes them to 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> # Using the syntax prior to NXLog EE 5, # where the port is defined in a separate directive. #<Input ssl> # Module im_ssl # ListenAddr localhost # Port 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>