Allowlists for Managing Incoming SIP Headers and Parameters
By default, the Oracle® Enterprise Session Border Controller (ESBC) ignores unknown SIP headers and URI parameters and passes them through. If you want the ESBC to accept only messages with headers and URI parameters complying with those supported by your internal equipment, you can use allowlists to control unknown headers and parameters in request and response traffic. An allowlist is an approved list of entities for which your equipment provides particular privileges, access, and recognition. The ESBC uses configured allowlist profiles to control and accept specific inbound SIP headers and URI parameters. When you configure this service, the ESBC rejects requests not matching the configured profile, or removes the headers or URI parameters not specified in the configured profile.
With allowlists, you can specify which SIP signaling messages you want to allow into your network and which messages to reject or delete. In the flow of SIP traffic to and from the ESBC, the ESBC matches any received request or response against the allowlist and rejects or deletes elements that do not match based on the actions specified in the allowlist configuration.
For responses, the ESBC does not reject the message if a header or parameter is not found in the allowlist even when the action is set to reject. Instead, the ESBC deletes the offending parameter or header. In addition, if the message is a request of the method type ACK, PRACK, CANCEL or BYE, the ESBC deletes all unmatched elements and does not reject the request even when the action is configured to reject.
The allowlist verification performs for any method, but you can narrow the list to operate only on specific methods by defining them in the methods parameter of the configuration.
Allowlist verification occurs when the ESBC receives a request or response, but only after the ESBC processes the inbound header manipulation rule (HMR), network management controls (NMC), Resource-Priority header (RPH), and monthly minutes checking.
The ESBC responds to requests with non-matching headers or parameters configured with an action of reject with a "403 Forbidden" response, by default. You can use a local-response event, allowed-elements-profile-rejection, to override the default reject status code and reason phrase.
The configured allowlist operates transparently on headers that contain multiple URIs or multiple header values within a single header (header values separated by a comma).
Parameter parsing operates only on parameters that it can identify. For parameters that cannot be parsed, for example an invalid URI (<sip:user@host.com&hp=val>), the ESBC ignores this URI header parameter value of "hp" because it is not contained within a valid URI. Although it might look like a URI header parameter, URI headers must come after URI parameters. Parameter matching does not occur if the headers and parameters in the URI are not well-formed. The ESBC does not remove the parameter just because it cannot identify it.
Allowlist Learning
You can build a SIP header and URI parameter allowlist configuration by way of the learning capabilities of the Oracle® Enterprise Session Border Controller (ESBC). When you enable learning mode on the ESBC, it acquires knowledge of the allowable headers and parameters currently coming into your network. The ESBC collects the information about the headers received and the parameters that exist within each header. The system gathers the information until you disable the learning mode.
After you disable the learning mode, the ESBC prompts you to enter a name for the allowed-elements-profile. If the profile name you entered does not exist, the ESBC writes the captured information to the new allowed-elements-profile configuration. The administrator can then make changes to the configuration as applicable, save the configuration, and apply it to a logical remote entity.
The allowed-elements-profile does not contain any wild card rules because the ESBC cannot generate wild card headers and parameters during the learning mode. The Methods object is populated from the list of methods seen by the ESBC while learning.
Note:
Oracle recommends running the learning mode during off-peak and light traffic periods. Learning mode can operate in conjunction with the execution of an allowed-elements-profile. The learning occurs just before any configured allowed-elements-profile configuration.Allowlist Learning Configuration
The ACLI interface provides two commands that allow a Superuser to start and stop allowlist learning on the Oracle® Enterprise Session Border Controller (ESBC):
Command | Description |
---|---|
start <argument> <options> | Starts allowlist learning on the ESBC.
You must specify the argument learn-allowed-elements with this command to start the learning operation. Optionally, you can use method, msg-type, and params after the argument. |
stop <argument> <identifier> | Stops the allowlist learning on the ESBC and writes the learned
configuration to the editing configuration on the ESBC where it is saved and
activated.
You must specify the argument learn-allowed-elements with this command to stop the learning operation. You must specify a unique identifier that identifies the allowed-elements-profile name.If you specify an identifier name that already exists as a profile, the ACLI returns an error message and prompts you to enter a different name. |
You can use these commands at the top level ACLI prompt as required on the ESBC.
You use these commands with the argument, learn-allowed-elements to start and stop allowlist learning. By default, the learning mode creates a single rule-set under which all of the headers and their respective parameters are stored.
For example:
ORACLE# start learn-allowed-elements
Learning mode for allowed-elements-profile started.
In the preceding example, start is the top level ACLI command and learn-allowed-elements is the operation being performed.
Optionally, you can specify [method], [msg-type], and [params] in any order, for the Oracle® Enterprise Session Border Controller to learn specific rule-set elements from incoming messages and save them to the allowlist configuration.
For example:
ORACLE# start learn-allowed-elements method msg-type params
The method option creates a new rule-set per unique method. The msg-type option creates a new rule-set per unique message-type seen. The params option performs URI and header parsing to examine parameters within the message. By default, parameter parsing is disabled.
Configure Allowlists for SIP Header and URI Parameter Management
You can configure allowlist profiles that tell the Oracle® Enterprise Session Border Controller (ESBC) to accept only inbound SIP headers and URI parameters that are configured in this allowlist. Using the allowed-elements-profile parameter, you can configure the settings for this parameter using the ACLI interface at session-router, enforcement-profile. Because the enforcement-profile object also pertains to session agents, realms, and SIP interfaces, you can also apply the enforcement profiles you configure to these entities. (Use the ACLI interface at session-router, session-agent, session-router, sip-interface, and media-manager, realm-config.)
The following configuration example assumes that your baseline configuration passes SIP traffic, with the ESBC in the role of an Access SBC. Use this procedure to configure a allowlist for the session router and optionally apply the specific allowlists to the session agent and SIP interface, as well as the media manager realm configuration.
The matched.log File
The matched.log file contains information about the timestamp, the received and sent ESBC network-interface, the IP address and port from which an incoming message was received, and which peer IP address and port it was received from or sent to. The log also specifies the request URI (if applicable), and the From, To, and Contact headers in the message, as well as which rule triggered the log action.
Dec 17 14:17:54.526 On [0:0]192.168.1.84:5060 sent to 192.168.1.60:5060
allowed-elements-profile[allowlist1(reject)]
INVITE sip:service@192.168.1.84:5060 SIP/2.0
From: sipp <sip:+2125551212@192.168.1.60:5060>;tag=3035SIPpTag001
To: sut <sip:service@192.168.1.84>
Contact: sip:sipp@192.168.1.60:5060
Rejected Messages Monitoring
Allowlists control whether or not the Oracle® Enterprise Session Border Controller (ESBC) accepts unknown headers and URI parameters in incoming request and response traffic. When the ESBC rejects messages according to the allowlist, the system logs the rejected messages a file called “matched.log,” if you set logging to enabled. You can open and view the log when you want to view the rejected messages.
In addition to sending rejected messages to the “matched.log” file, the system sends rejected messages through a burst counter that keeps track of the number of messages rejected. You can enter the show sipd command to display the number of rejected messages. The counter is titled Rejected Message.
Configuration Exception
In certain circumstances, the Oracle® Enterprise Session Border Controller (ESBC) ignores specific parameters in incoming Request-URI messages and automatically adds header-rules.
In a Request-URI, all parameters are URI parameters and URI headers are not allowed. If you define values for the “allow-header-param”, “allow-uri-header-name”, and “allow-uri-param”, the ESBC ignores these parameters in the Request-URI. Instead, the ESBC automatically adds header-rules for incoming “Via”, “From”, To”, “Call-ID”, and “CSeq” messages. These are explicit header rules that you cannot delete. Each header-rule in a Request-URI includes parameters populated with the value of *. If required, you can change the header-rule parameter values with the values identified in the following table.
Header Rule | Applicable Parameter | Required Value(s) |
---|---|---|
Via | allow-header-param |
|
From | allow-header-param |
|
To | allow-header-param |
|
Call-ID | allow-header-param | No restrictions |
CSeq | allow-header-param | No restrictions |
Verify Allowlist Configuration
After you configure and save an allowlist on the Oracle® Enterprise Session Border Controller (ESBC), you can use the verify-config command at the top level prompt to verify the saved configuration: For example:
ORACLE# verify-config
The verify-config command checks for errors in the ESBC configuration. Allowlist configuration errors specifically related to the enforcement-profile object also display in the output of this command when applicable. The allowlist configuration errors display if any references to the allowed-element-profiles are improperly configured. If errors exist, the system displays the following message:
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ERROR: enforcement-profile [ep] contains a reference to an allowed-enforcement-profile [abc] that does not exist
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