140.32. TLS/SSL (im_ssl)

Table of Contents

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.

Note	To examine the supported platforms, see the list of installer packages in the Available Modules chapter.

140.32.1. Configuration

The im_ssl module accepts the following directives in addition to the common module directives.

ListenAddr: The module accepts connections on the IP address or hostname and port defined here. The default address is localhost and 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.

Important

Formerly called Host, this directive is now ListenAddr. Host will become deprecated from NXLog EE 6.0 for incoming traffic.

Note	When a hostname is used as the `ListenAddr`, the corresponding IP address is only resolved when the module starts up. The listening socket will be bound to that IP addresses until the module is restarted, regardless of any DNS changes to the hostname.

Note

When the ListenAddr (or similar) directive specifies a hostname, the module binds to the first IP address that is exposed by the system for that hostname. On most systems that support IPv6, this address will be an IPv6 address. This means that client applications and the systems they run on will also need to have IPv6 support enabled, and must be able to connect to the same IPv6 address. NXLog output modules achieve this requirement through failover. For third-party client applications, the configuration details are application-specific but they should have the ability to detect which IP address the server is listening on when using a hostname to connect.

For client applications that don’t support IPv6, to avoid the behavior described above the ListenAddr directive of the listening module may be set to an IPv4 address e.g. 0.0.0.0.

Alternatively, the server-side system may be configured to prioritize IPv4 addresses for the hostname specified by the ListenAddr directive, although this is a more complicated and potentially intrusive approach. On most Linux-based systems, this can be achieved through the /etc/gai.conf configuration file. On BSD-based systems, the ip6addrctl command can be used. Windows is more limited and can only be configured to prioritize IPv4 over IPv6 addresses for ALL hostnames resolved on the system, by setting the following registry value to 0x20:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\DisabledComponents

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.

Port: The module listens for incoming connections on the port defined in this directive. The default is port 514.

Important

The Port directive will become deprecated from NXLog EE 6.0. After that, the port can only be defined in the ListenAddr directive.

AllowIP

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 (IPv4 address)
0.0.0.0/32 (IPv4 network with subnet bits)
0.0.0.0/0.0.0.0 (IPv4 network with subnet address)
aa::1 (IPv6 address)
aa::12/64 (IPv6 network with subnet bits)

AllowUntrusted: This boolean directive specifies that the remote connection should be allowed without certificate verification. If set to TRUE the remote will be able to connect with an unknown or self-signed certificate. The default value is FALSE: all connections must present a trusted certificate.

CADir: This specifies the path to a directory containing certificate authority (CA) certificates, which will be used to check the certificate of the remote socket. The certificate filenames in this directory must be in the OpenSSL hashed format. A remote’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.

CAFile: This specifies the path of the certificate authority (CA) certificate, which will be used to check the certificate of the remote socket. To trust a self-signed certificate presented by the remote (which is not signed by a CA), provide that certificate instead.

CAThumbprint: This optional directive specifies the certificate thumbprint of the certificate authority (CA), which is used to look up the CA certificate from the Windows certificate store. The hexadecimal fingerprint string can be copied straight from Windows Certificate Manager (certmgr.msc), whitespaces are automatically removed. This directive is only supported on Windows. This directive and the CADir and CAFile directives are mutually exclusive.

CertFile: This specifies the path of the certificate file to be used for the SSL handshake.

CertKeyFile: This specifies the path of the certificate key file to be used for the SSL handshake.

CertThumbprint: This optional directive specifies the certificate thumbprint to be used for the SSL handshake. The hexadecimal fingerprint string can be copied straight from Windows Certificate Manager (certmgr.msc), whitespaces are automatically removed. This directive is only supported on Windows. This directive and the CertFile and CertKeyFile directives are mutually exclusive.

KeyPass: With this directive, a password can be supplied for the certificate key file defined in CertKeyFile. This directive is not needed for passwordless private keys.

CRLDir: This specifies the path to a directory containing certificate revocation lists (CRLs), which will be consulted when checking the certificate of the remote socket. The certificate filenames in this directory must be in the OpenSSL hashed format.

CRLFile: This specifies the path of the certificate revocation list (CRL) which will be consulted when checking the certificate of the remote socket.

DHFile: This optional directive specifies file with dh-parameters for Diffie-Hellman key exchange. These parameters can be generated with dhparam(1ssl). If no directive is specified, default parameters will be used. See OpenSSL Wiki for greater details.

RequireCert: This boolean value specifies that the remote must present a certificate. If set to TRUE and there is no certificate presented during the connection handshake, the connection will be refused. The default value is TRUE: each connection must use a certificate.

SSLCipher: This optional directive can be used to set the permitted SSL cipher list, overriding the default. Use the format described in the ciphers(1ssl) man page.

Note	If RSA or DSA ciphers with Diffie-Hellman key exchange are used, DHFile can be set for specifying custom dh-parameters.

SSLCiphersuites: This optional directive can be used to define the permitted SSL cipher list in case the SSLProtocol directive is set to TLSv1.3. Use the same format as in the SSLCipher directive.

SSLCompression

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 (the compression is disabled).

Note	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.

SSLProtocol: 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: SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, and TLSv1.3. By default, the TLSv1.2 and TLSv1.3 protocols are allowed. Note that the OpenSSL library shipped by Linux distributions may not support SSLv2 and SSLv3, and these will not work even if enabled with this directive.

140.32.2. Fields

The following fields are used by im_ssl.

$raw_event (type: string): The received string.

$MessageSourceAddress (type: string): The IP address of the remote host.

140.32.3. Examples

Pre-v5 syntax examples are included, they will become invalid with NXLog EE 6.0.

Example 790. Accepting binary logs from another NXLog agent

This configuration accepts secured log messages in the NXLog binary format and writes them to file.

nxlog.conf


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  <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>

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140.32. TLS/SSL (im_ssl) | Log Collection Solutions