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What
Address XML vulnerabilities and minimize attacks on your API. Optionally, detect XML payload attacks based on configured limits. Screen against XML threats using the following approaches:
- Validate messages against an XML schema (
.xsd
) - Evaluate message content for specific keywords or patterns to exclude
- Detect corrupt or malformed messages before those messages are parsed
Element reference
The element reference describes the elements and attributes of the XMLThreatProtection policy.
<XMLThreatProtection async="false" continueOnError="false" enabled="true" name="XML-Threat-Protection-1"> <DisplayName>XML Threat Protection 1</DisplayName> <NameLimits> <Element>10</Element> <Attribute>10</Attribute> <NamespacePrefix>10</NamespacePrefix> <ProcessingInstructionTarget>10</ProcessingInstructionTarget> </NameLimits> <Source>request</Source> <StructureLimits> <NodeDepth>5</NodeDepth> <AttributeCountPerElement>2</AttributeCountPerElement> <NamespaceCountPerElement>3</NamespaceCountPerElement> <ChildCount includeComment="true" includeElement="true" includeProcessingInstruction="true" includeText="true">3</ChildCount> </StructureLimits> <ValueLimits> <Text>15</Text> <Attribute>10</Attribute> <NamespaceURI>10</NamespaceURI> <Comment>10</Comment> <ProcessingInstructionData>10</ProcessingInstructionData> </ValueLimits> </XMLThreatProtection>
<XMLThreatProtection> attributes
<XMLThreatProtection async="false" continueOnError="false" enabled="true" name="XML-Threat-Protection-1">
The following table describes attributes that are common to all policy parent elements:
Attribute | Description | Default | Presence |
---|---|---|---|
name |
The internal name of the policy. The value of the Optionally, use the |
N/A | Required |
continueOnError |
Set to Set to |
false | Optional |
enabled |
Set to Set to |
true | Optional |
async |
This attribute is deprecated. |
false | Deprecated |
<DisplayName> element
Use in addition to the name
attribute to label the policy in the
management UI proxy editor with a different, natural-language name.
<DisplayName>Policy Display Name</DisplayName>
Default |
N/A If you omit this element, the value of the policy's |
---|---|
Presence | Optional |
Type | String |
<NameLimits> element
Specifies character limits to be checked and enforced by the policy.
<NameLimits> <Element>10</Element> <Attribute>10</Attribute> <NamespacePrefix>10</NamespacePrefix> <ProcessingInstructionTarget>10</ProcessingInstructionTarget> </NameLimits>
Default: | N/A |
Presence: | Optional |
Type: | N/A |
<NameLimits>/<Element> element
Specifies a limit on the maximum number of characters permitted in any element name in the XML document.
For example, consider the following XML:
<book category="WEB"> <title>Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> </book>
When analyzing the XML above, the <Element>
element value in the policy
snippet below will validate that element names (book
, title
,
author
, and year)
do not exceed 10
characters.
<NameLimits> <Element>10</Element> <Attribute>10</Attribute> <NamespacePrefix>10</NamespacePrefix> <ProcessingInstructionTarget>10</ProcessingInstructionTarget> </NameLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: | Integer |
<NameLimits>/<Attribute> element
Specifies a limit on the maximum number of characters permitted in any attribute name in the XML document.
For example, consider the following XML:
<book category="WEB"> <title>Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> </book>
When analyzing the XML above, the <Attribute>
element value in the policy
snippet below will validate that attribute name category
does not exceed
10
characters.
<NameLimits> <Element>10</Element> <Attribute>10</Attribute> <NamespacePrefix>10</NamespacePrefix> <ProcessingInstructionTarget>10</ProcessingInstructionTarget> </NameLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: | Integer |
<NameLimits>/<NamespacePrefix> element
Specifies a limit on the maximum number of characters permitted in the namespace prefix in the XML document.
For example, consider the following XML:
<ns1:myelem xmlns:ns1="http://ns1.com"/>
When analyzing the XML above, the <NamespacePrefix>
element value in the
policy snippet below will validate that the namespace prefix ns1
does not exceed
10
characters.
<NameLimits> <Element>10</Element> <Attribute>10</Attribute> <NamespacePrefix>10</NamespacePrefix> <ProcessingInstructionTarget>10</ProcessingInstructionTarget> </NameLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: | Integer |
<NameLimits>/<ProcessingInstructionTarget> element
Specifies a limit on the maximum number of characters permitted in the target of any processing instructions in the XML document.
For example, consider the following XML:
<?xml-stylesheet type="text/xsl" href="style.xsl"?>
When analyzing the XML above, the <ProcessingInstructionTarget>
element
value in the policy snippet below will validate that the processing instruction target
xml-stylesheet
does not exceed 10
characters.
<NameLimits> <Element>10</Element> <Attribute>10</Attribute> <NamespacePrefix>10</NamespacePrefix> <ProcessingInstructionTarget>10</ProcessingInstructionTarget> </NameLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: | Integer |
<Source> element
Message to be screened for XML payload attacks. This is most commonly set to
request
, as you will typically need to validate inbound requests from client apps.
When set to message
, this element will automatically evaluate the request message
when attached to the request flow and the response message when attached to the response
flow.
<Source>request</Source>
Default: | request |
Presence: | Optional |
Type: |
String. Select from |
<StructuralLimits> element
Specifies structural limits to be checked and enforced by the policy.
<StructureLimits> <NodeDepth>5</NodeDepth> <AttributeCountPerElement>2</AttributeCountPerElement> <NamespaceCountPerElement>3</NamespaceCountPerElement> <ChildCount includeComment="true" includeElement="true" includeProcessingInstruction="true" includeText="true">3</ChildCount> </StructureLimits>
Default: | N/A |
Presence: | Optional |
Type: | N/A |
<StructuralLimits>/<NodeDepth> element
Specifies the maximum node depth allowed in the XML.
<StructureLimits> <NodeDepth>5</NodeDepth> <AttributeCountPerElement>2</AttributeCountPerElement> <NamespaceCountPerElement>3</NamespaceCountPerElement> <ChildCount includeComment="true" includeElement="true" includeProcessingInstruction="true" includeText="true">3</ChildCount> </StructureLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: |
Integer |
<StructuralLimits>/<AttributeCountPerElement> element
Specifies the maximum number of attributes allowed for any element.
For example, consider the following XML:
<book category="WEB"> <title>Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> </book>When analyzing the XML above, the
<AttributeCountPerElement>
element value
in the policy snippet below will validate that the elements book
, title
,
author
, and year
do not have more than 2
attributes each.
Note that attributes used for defining namespaces are not counted.
<StructureLimits> <NodeDepth>5</NodeDepth> <AttributeCountPerElement>2</AttributeCountPerElement> <NamespaceCountPerElement>3</NamespaceCountPerElement> <ChildCount includeComment="true" includeElement="true" includeProcessingInstruction="true" includeText="true">3</ChildCount> </StructureLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: |
Integer |
<StructuralLimits>/<NameSpaceCountPerElement> element
Specifies the maximum number of namespace definitions allowed for any element.
For example, consider the following XML:
<e1 attr1="val1" attr2="val2"> <e2 xmlns="http://apigee.com" xmlns:yahoo="http://yahoo.com" one="1" yahoo:two="2"/> </e1>
When analyzing the XML above, the <NamespaceCountPerElement>
element value
in the policy snippet below will validate that the elements e1
and e2
do not have more than 2
namespace definitions each. In this case, <e1> has 0 namespace definitions and
<e2> has 2 namespace
definitions: xmlns="http://apigee.com"
and
xmlns:yahoo="http://yahoo.com"
.
<StructureLimits> <NodeDepth>5</NodeDepth> <AttributeCountPerElement>2</AttributeCountPerElement> <NamespaceCountPerElement>3</NamespaceCountPerElement> <ChildCount includeComment="true" includeElement="true" includeProcessingInstruction="true" includeText="true">3</ChildCount> </StructureLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: |
Integer |
<StructuralLimits>/<ChildCount> element
Specifies the maximum number of child elements allowed for any element.
<StructureLimits> <NodeDepth>5</NodeDepth> <AttributeCountPerElement>2</AttributeCountPerElement> <NamespaceCountPerElement>3</NamespaceCountPerElement> <ChildCount includeComment="true" includeElement="true" includeProcessingInstruction="true" includeText="true">3</ChildCount> </StructureLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: |
Integer |
Attributes
Attribute | Default | Presence |
---|---|---|
includeComment | true | Optional |
includeElement | true | Optional |
includeProcessingInstructions | true | Optional |
includeText | true | Optional |
<ValueLimits> element
Specifies character limits for values to be checked and enforced by the policy.
<ValueLimits> <Text>15</Text> <Attribute>10</Attribute> <NamespaceURI>10</NamespaceURI> <Comment>10</Comment> <ProcessingInstructionData>10</ProcessingInstructionData> </ValueLimits>
Default: | N/A |
Presence: | Optional |
Type: |
N/A |
<ValueLimits>/<Text> element
Specifies a character limit for any text nodes present in the XML document.
For example, consider the following XML:
<book category="WEB"> <title>Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> </book>When analyzing the XML above, the
<Text>
element value in the policy
snippet below will validate that the element text values Learning XML
, Erik T.
Ray,
and 2003
do not exceed 15
characters each.
<ValueLimits> <Text>15</Text> <Attribute>10</Attribute> <NamespaceURI>10</NamespaceURI> <Comment>10</Comment> <ProcessingInstructionData>10</ProcessingInstructionData> </ValueLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: |
Integer |
<ValueLimits>/<Attribute> element
Specifies a character limit for any attribute values present in the XML document.
For example, consider the following XML:
<book category="WEB"> <title>Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> </book>When analyzing the XML above, the
<Attribute>
element value in the policy
snippet below will validate that the attribute value WEB
does not exceed
10
characters.
<ValueLimits> <Text>15</Text> <Attribute>10</Attribute> <NamespaceURI>10</NamespaceURI> <Comment>10</Comment> <ProcessingInstructionData>10</ProcessingInstructionData> </ValueLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: |
Integer |
<ValueLimits>/<NamespaceURI> element
Specifies a character limit for any namespace URIs present in the XML document.
For example, consider the following XML:
<ns1:myelem xmlns:ns1="http://ns1.com"/>When analyzing the XML above, the
<NamespaceURI>
element value in the
policy snippet below will validate that the namespace URI value http://ns1.com
does
not exceed 10
characters.
<ValueLimits> <Text>15</Text> <Attribute>10</Attribute> <NamespaceURI>10</NamespaceURI> <Comment>10</Comment> <ProcessingInstructionData>10</ProcessingInstructionData> </ValueLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: |
Integer |
<ValueLimits>/<Comment> element
Specifies a character limit for any comments present in the XML document.
For example, consider the following XML:
<book category="WEB"> <!-- This is a comment --> <title>Learning XML</title> <author>Erik T. Ray</author> <year>2003</year> </book>When analyzing the XML above, the
<Comment>
element value in the policy
snippet below will validate that the comment text This is a comment
does not exceed
10
characters.
<ValueLimits> <Text>15</Text> <Attribute>10</Attribute> <NamespaceURI>10</NamespaceURI> <Comment>10</Comment> <ProcessingInstructionData>10</ProcessingInstructionData> </ValueLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: |
Integer |
<ValueLimits>/<ProcessingInstructionData> element
Specifies a character limit for any processing instruction text present in the XML document.
For example, consider the following XML:
<?xml-stylesheet type="text/xsl" href="style.xsl"?>When analyzing the XML above, the
<ProcessingInstructionData>
element
value in the policy snippet below will validate that the processing instruction text
type="text/xsl" href="style.xsl"
does not exceed 10
characters.
<ValueLimits> <Text>15</Text> <Attribute>10</Attribute> <NamespaceURI>10</NamespaceURI> <Comment>10</Comment> <ProcessingInstructionData>10</ProcessingInstructionData> </ValueLimits>
Default: | If you do not specify a limit, the system applies a default value of -1 ,
which the system equates to no limit. |
Presence: | Optional |
Type: |
Integer |
Error reference
This section describes the fault codes and error messages that are returned and fault variables that are set by Edge when this policy triggers an error. This information is important to know if you are developing fault rules to handle faults. To learn more, see What you need to know about policy errors and Handling faults.
Runtime errors
These errors can occur when the policy executes.
Fault code | HTTP status | Cause | Fix |
---|---|---|---|
steps.xmlthreatprotection.ExecutionFailed |
500 | The XMLThreatProtection policy can throw many different types of ExecutionFailed errors. Most of these errors occur when a specific threshold set in the policy is exceeded. These types of errors include: element name length, child count, node depth, attribute count, attribute name length, and many others. You can see the complete list in the XMLThreatProtection policy runtime error troubleshooting topic. | build |
steps.xmlthreatprotection.InvalidXMLPayload |
500 |
This error occurs if the input message payload specified by the XMLThreatProtection policy's <Source> element is not a valid XML Document.
|
build |
steps.xmlthreatprotection.SourceUnavailable |
500 |
This error occurs if the message
variable specified in the <Source> element is either:
|
build |
steps.xmlthreatprotection.NonMessageVariable |
500 |
This error occurs if the <Source> element is set to a variable which
is not of type
message.
|
build |
Notes:
- The error name ExecutionFailed is the default error name and will be returned regardless of the type of error detected; however, this default can be changed by setting an organization-level property. When this property is set, the error name will reflect the actual error. For example, "TextExceeded" or "AttrValueExceeded". See Usage Notes for details.
- The 500 HTTP status is the default; however, the HTTP Status can be changed to 400 for request flow faults by setting an organization-level property. See Usage Notes for details.
Deployment errors
None.
Fault variables
These variables are set when a runtime error occurs. For more information, see What you need to know about policy errors.
Variables | Where | Example |
---|---|---|
fault.name="fault_name" |
fault_name is the name of the fault, as listed in the Runtime errors table above. The fault name is the last part of the fault code. | fault.name Matches "SourceUnavailable" |
xmlattack.policy_name.failed |
policy_name is the user-specified name of the policy that threw the fault. | xmlattack.XPT-SecureRequest.failed = true |
Example error response
{ "fault": { "faultstring": "XMLThreatProtection[XPT-SecureRequest]: Execution failed. reason: XMLThreatProtection[XTP-SecureRequest]: Exceeded object entry name length at line 2", "detail": { "errorcode": "steps.xmlthreatprotection.ExecutionFailed" } } }
Example fault rule
<FaultRule name="XML Threat Protection Policy Faults"> <Step> <Name>AM-CustomErrorResponse</Name> <Condition>(fault.name Matches "ExecutionFailed") </Condition> </Step> <Condition>(xmlattack.XPT-SecureRequest.failed = true) </Condition> </FaultRule>
Schemas
Usage notes
Any server that receives online data is subject to attack, whether malicious or unintentional. Some attacks take advantage of the flexibility of XML by constructing invalid documents that have the potential to compromise back-end systems. Corrupt or extremely complex XML documents can cause servers to allocate more memory than is available, tying up CPU and memory resources, crashing parsers, and generally disabling message processing and creating application-level denial-of-service attacks.
Threat protection error configuration
Important information if you are creating FaultRules for this policy: By
default, Edge throws an HTTP 500 Internal Server Error status code and an ExecutionFailed error
code if a message doesn't make it past a JSON or XML Threat Protection policy. You can change
that error behavior with a new organization-level property. When setting org
property features.isPolicyHttpStatusEnabled
to true, the following
behavior occurs:
- Request: With a threat protection policy attached to any request flow, invalid messages return a 400 Bad Request status code, along with a corresponding policy error code (rather than just ExecutionFailed).
- Response: With a threat protection policy attached to any response flow, invalid messages still return a 500 Internal Server Error status code, and one of the corresponding policy error codes is thrown (rather than just ExecutionFailed).
Cloud customers must contact Apigee Edge Support to set the organization property.