Rest Cheat Sheet

Rest Api Cheat Sheet
Rest Assured Cheat Sheet
The Cheat Sheet Jobs

Probably the Best Regular Expression Cheat Sheet on the Net. The most commonly used metacharacters in Python, PHP, Perl, JavaScript, and Ruby. Download as PDF. Metacharacter Meaning n. Rest of the line is treated as a comment in x mode.
REST Cheat Sheet. January 9, 2013 by jdslo. Representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation.
Strategy and Design Guidelines for REST APIs and Platform Building - REST Cheat Sheets.

REST stands for Sign in. RESTful API Cheat Sheet. As you can see, the 7 Restful Routes are the foundation for building any CRUD app. I hope this cheat sheet was helpful for creating your own.

It evolved as Fielding wrote the HTTP/1.1 and URI specs and has been proven to be well-suited for developing distributed hypermedia applications. While REST is more widely applicable, it is most commonly used within the context of communicating with services via HTTP.

The primary connector types are client and server, secondary connectors include cache, resolver and tunnel.

REST APIs are stateless. Stateful APIs do not adhere to the REST architectural style. State in the REST acronym refers to the state of the resource which the API accesses, not the state of a session within which the API is called. While there may be good reasons for building a stateful API, it is important to realize that managing sessions is complex and difficult to do securely.

Stateful services are out of scope of this Cheat Sheet: Passing state from client to backend, while making the service technically stateless, is an anti-pattern that should also be avoided as it is prone to replay and impersonation attacks.

In order to implement flows with REST APIs, resources are typically created, read, updated and deleted. For example, an ecommerce site may offer methods to create an empty shopping cart, to add items to the cart and to check out the cart. Each of these REST calls is stateless and the endpoint should check whether the caller is authorized to perform the requested operation.

Another key feature of REST applications is the use of standard HTTP verbs and error codes in the pursuit or removing unnecessary variation among different services.

Another key feature of REST applications is the use of HATEOAS or Hypermedia As The Engine of Application State. This provides REST applications a self-documenting nature making it easier for developers to interact with a REST service without a priori knowledge.

Secure REST services must only provide HTTPS endpoints. This protects authentication credentials in transit, for example passwords, API keys or JSON Web Tokens. It also allows clients to authenticate the service and guarantees integrity of the transmitted data.

See the Transport Layer Protection Cheat Sheet for additional information.

Consider the use of mutually authenticated client-side certificates to provide additional protection for highly privileged web services.

Non-public REST services must perform access control at each API endpoint. Web services in monolithic applications implement this by means of user authentication, authorisation logic and session management. This has several drawbacks for modern architectures which compose multiple micro services following the RESTful style.

in order to minimise latency and reduce coupling between services, the access control decision should be taken locally by REST endpoints
user authentication should be centralised in a Identity Provider (IdP), which issues access tokens

There seems to be a convergence towards using JSON Web Tokens (JWT) as the format for security tokens. JWTs are JSON data structures containing a set of claims that can be used for access control decisions. A cryptographic signature or message authentication code (MAC) can be used to protect the integrity of the JWT.

Rest Api Cheat Sheet

Ensure JWTs are integrity protected by either a signature or a MAC. Do not allow the unsecured JWTs: {'alg':'none'}.
- See here
In general, signatures should be preferred over MACs for integrity protection of JWTs.

If MACs are used for integrity protection, every service that is able to validate JWTs can also create new JWTs using the same key. This means that all services using the same key have to mutually trust each other. Another consequence of this is that a compromise of any service also compromises all other services sharing the same key. See here for additional information.

The relying party or token consumer validates a JWT by verifying its integrity and claims contained.

A relying party must verify the integrity of the JWT based on its own configuration or hard-coded logic. It must not rely on the information of the JWT header to select the verification algorithm. See here and here

Some claims have been standardised and should be present in JWT used for access controls. At least the following of the standard claims should be verified:

iss or issuer - is this a trusted issuer? Is it the expected owner of the signing key?
aud or audience - is the relying party in the target audience for this JWT?
exp or expiration time - is the current time before the end of the validity period of this token?
nbf or not before time - is the current time after the start of the validity period of this token?

Public REST services without access control run the risk of being farmed leading to excessive bills for bandwidth or compute cycles. API keys can be used to mitigate this risk. They are also often used by organisation to monetize APIs; instead of blocking high-frequency calls, clients are given access in accordance to a purchased access plan.

API keys can reduce the impact of denial-of-service attacks. However, when they are issued to third-party clients, they are relatively easy to compromise.

Require API keys for every request to the protected endpoint.
Return 429 Too Many Requests HTTP response code if requests are coming in too quickly.
Revoke the API key if the client violates the usage agreement.
Do not rely exclusively on API keys to protect sensitive, critical or high-value resources.

Apply a whitelist of permitted HTTP Methods e.g. GET, POST, PUT.
Reject all requests not matching the whitelist with HTTP response code 405 Method not allowed.
Make sure the caller is authorised to use the incoming HTTP method on the resource collection, action, and record

Rest Assured Cheat Sheet

In Java EE in particular, this can be difficult to implement properly. See Bypassing Web Authentication and Authorization with HTTP Verb Tampering for an explanation of this common misconfiguration.

Do not trust input parameters/objects.
Validate input: length / range / format and type.
Achieve an implicit input validation by using strong types like numbers, booleans, dates, times or fixed data ranges in API parameters.
Constrain string inputs with regexps.
Reject unexpected/illegal content.
Make use of validation/sanitation libraries or frameworks in your specific language.
Define an appropriate request size limit and reject requests exceeding the limit with HTTP response status 413 Request Entity Too Large.
Consider logging input validation failures. Assume that someone who is performing hundreds of failed input validations per second is up to no good.
Have a look at input validation cheat sheet for comprehensive explanation.
Use a secure parser for parsing the incoming messages. If you are using XML, make sure to use a parser that is not vulnerable to XXE_Processing) and similar attacks.

A REST request or response body should match the intended content type in the header. Otherwise this could cause misinterpretation at the consumer/producer side and lead to code injection/execution.

Document all supported content types in your API.

Validate request content types

Reject requests containing unexpected or missing content type headers with HTTP response status 406 Unacceptable or 415 Unsupported Media Type.
For XML content types ensure appropriate XML parser hardening, see the XXE cheat sheet.
Avoid accidentally exposing unintended content types by explicitly defining content types e.g. Jersey (Java) @consumes('application/json'); @produces('application/json'). This avoids XXE-attack_Processing) vectors for example.

Send safe response content types

It is common for REST services to allow multiple response types (e.g. application/xml or application/json, and the client specifies the preferred order of response types by the Accept header in the request.

Do NOT simply copy the Accept header to the Content-type header of the response.
Reject the request (ideally with a 406 Not Acceptable response) if the Accept header does not specifically contain one of the allowable types.

Services including script code (e.g. JavaScript) in their responses must be especially careful to defend against header injection attack.

Ensure sending intended content type headers in your response matching your body content e.g. application/json and not application/javascript.

Avoid exposing management endpoints via Internet.
If management endpoints must be accessible via the Internet, make sure that users must use a strong authentication mechanism, e.g. multi-factor.
Expose management endpoints via different HTTP ports or hosts preferably on a different NIC and restricted subnet.
Restrict access to these endpoints by firewall rules or use of access control lists.

Respond with generic error messages - avoid revealing details of the failure unnecessarily.
Do not pass technical details (e.g. call stacks or other internal hints) to the client.

Write audit logs before and after security related events.
Consider logging token validation errors in order to detect attacks.
Take care of log injection attacks by sanitising log data beforehand.

To make sure the content of a given resources is interpreted correctly by the browser, the server should always send the Content-Type header with the correct content type, and preferably the Content-Type header should include a charset. The server should also send the X-Content-Type-Options: nosniffsecurity header to make sure the browser does not try to detect a different Content-Type than what is actually sent (can lead to XSS).

Additionally the client should send the X-Frame-Options: denysecurity header to protect against drag'n drop clickjacking attacks in older browsers.

Cross-Origin Resource Sharing (CORS) is a W3C standard to flexibly specify what cross-domain requests are permitted. By delivering appropriate CORS Headers your REST API signals to the browser which domains, AKA origins, are allowed to make JavaScript calls to the REST service.

Disable CORS headers if cross-domain calls are not supported/expected.
Be as specific as possible and as general as necessary when setting the origins of cross-domain calls.

RESTful web services should be careful to prevent leaking credentials. Passwords, security tokens, and API keys should not appear in the URL, as this can be captured in web server logs, which makes them intrinsically valuable.

In POST/PUT requests sensitive data should be transferred in the request body or request headers.
In GET requests sensitive data should be transferred in an HTTP Header.

OK:

https://example.com/resourceCollection/[ID]/action

https://twitter.com/vanderaj/lists

Dcfc twitter. NOT OK:

https://example.com/controller/123/action?apiKey=a53f435643de32 because API Key is into the URL.

HTTP defines status code. When designing REST API, don't just use 200 for success or 404 for error. Always use the semantically appropriate status code for the response.

Here is a non-exhaustive selection of security related REST API status codes. Use it to ensure you return the correct code.

Code	Message	Decription
200	OK	Response to a successful REST API action. The HTTP method can be GET, POST, PUT, PATCH or DELETE.
201	Created	The request has been fulfilled and resource created. A URI for the created resource is returned in the Location header.
202	Accepted	The request has been accepted for processing, but processing is not yet complete.
301	Moved Permanently	Permanent redirection.
304	Not Modified	Caching related response that returned when the client has the same copy of the resource as the server.
307	Temporary Redirect	Temporary redirection of resource.
400	Bad Request	The request is malformed, such as message body format error.
401	Unauthorized	Wrong or no authentication ID/password provided.
403	Forbidden	It's used when the authentication succeeded but authenticated user doesn't have permission to the request resource.
404	Not Found	When a non-existent resource is requested.
405	Method Not Acceptable	The error for an unexpected HTTP method. For example, the REST API is expecting HTTP GET, but HTTP PUT is used.
406	Unacceptable	The client presented a content type in the Accept header which is not supported by the server API.
413	Payload too large	Use it to signal that the request size exceeded the given limit e.g. regarding file uploads.
415	Unsupported Media Type	The requested content type is not supported by the REST service.
429	Too Many Requests	The error is used when there may be DOS attack detected or the request is rejected due to rate limiting.
500	Internal Server Error	An unexpected condition prevented the server from fulfilling the request. Be aware that the response should not reveal internal information that helps an attacker, e.g. detailed error messages or stack traces.
501	Not Implemented	The REST service does not implement the requested operation yet.
503	Service Unavailable	The REST service is temporarily unable to process the request. Used to inform the client it should retry at a later time.

Additional information about HTTP return code usage in REST API can be found here and here.

Erlend Oftedal - erlend.oftedal@owasp.org

Andrew van der Stock - vanderaj@owasp.org

Tony Hsu Hsiang Chih- Hsiang_chihi@yahoo.com

Johan Peeters - yo@johanpeeters.com

Jan Wolff - jan.wolff@owasp.org

Rocco Gränitz - rocco.graenitz@owasp.org

Manh Pham - manhpt2811@gmail.com

Last revision (mm/dd/yy): 09/4/2018

8Validate content types
12Security headers

REST (or REpresentational State Transfer) is an architectural style first described in Roy Fielding's Ph.D. dissertation on Architectural Styles and the Design of Network-based Software Architectures. It evolved as Fielding wrote the HTTP/1.1 and URI specs and has been proven to be well-suited for developing distributed hypermedia applications. While REST is more widely applicable, it is most commonly used within the context of communicating with services via HTTP.

The key abstraction of information in REST is a resource. A REST API resource is identified by a URI, usually a HTTP URL. REST components use connectors to perform actions on a resource by using a representation to capture the current or intended state of the resource and transferring that representation. The primary connector types are client and server, secondary connectors include cache, resolver and tunnel. In order to implement flows with REST APIs, resources are typically created, read, updated and deleted. For example, an ecommerce site may offer methods to create an empty shopping cart, to add items to the cart and to check out the cart.

Another key feature of REST applications is the use of standard HTTP verbs and error codes in the pursuit or removing unnecessary variation among different services.

Another key feature of REST applications is the use of HATEOS or Hypermedia as the Engine of Application State. This provides REST applications a self-documenting nature making it easier for developers to interact with a REST service without a priori knowledge.

See the Transport Layer Protection Cheat Sheet for additional information.

Consider the use of mutually authenticated client-side certificates to provide additional protection for highly privileged web services.

in order to minimise latency and reduce coupling between services, the access control decision should be taken locally by REST endpoints
user authentication should be centralised in a Identity Provider (IdP), which issues access tokens

Ensure JWTs are integrity protected by either a signature or a MAC. Do not allow the unsecured JWTs: {'alg':'none'}. See https://tools.ietf.org/html/rfc7519#section-6.1
In general, signatures should be preferred over MACs for integrity protection of JWTs.

The relying party or token consumer validates a JWT by verifying its integrity and claims contained.

A relying party must verify the integrity of the JWT based on its own configuration or hard-coded logic. It must not rely on the information of the JWT header to select the verification algorithm. See https://www.chosenplaintext.ca/2015/03/31/jwt-algorithm-confusion.html and https://www.youtube.com/watch?v=bW5pS4e_MX8

Some claims have been standardised and should be present in JWT used for access controls. At least the following of the standard claims should be verified:

'iss' or issuer - is this a trusted issuer? Is it the expected owner of the signing key?
'aud' or audience - is the relying party in the target audience for this JWT?
'exp' or expiration time - is the current time before the end of the validity period of this token?
'nbf' or not before time - is the current time after the start of the validity period of this token?

API keys can reduce the impact of denial-of-service attacks. However, when they are issued to third-party clients, they are relatively easy to compromise.

Require API keys for every request to the protected endpoint.
Return 429 'Too Many Requests' HTTP response code if requests are coming in too quickly.
Revoke the API key if the client violates the usage agreement.
Do not rely exclusively on API keys to protect sensitive, critical or high-value resources.

Apply a whitelist of permitted HTTP Methods e.g. GET, POST, PUT

Reject all requests not matching the whitelist with HTTP response code 405 Method not allowed
Make sure the caller is authorised to use the incoming HTTP method on the resource collection, action, and record

In Java EE in particular, this can be difficult to implement properly. See Bypassing Web Authentication and Authorization with HTTP Verb Tampering for an explanation of this common misconfiguration.

Do not trust input parameters/objects
Validate input: length / range / format and type
Achieve an implicit input validation by using strong types like numbers, booleans, dates, times or fixed data ranges in API parameters
Constrain string inputs with regexps
Reject unexpected/illegal content
Make use of validation/sanitation libraries or frameworks in your specific language
Define an appropriate request size limit and reject requests exceeding the limit with HTTP response status 413 Request Entity Too Large
Consider logging input validation failures. Assume that someone who is performing hundreds of failed input validations per second is up to no good.
Have a look at input validation cheat sheet for comprehensive explanation

Use a secure parser for parsing the incoming messages. If you are using XML, make sure to use a parser that is not vulnerable to XXE and similar attacks.

A REST request or response body should match the intended content type in the header. Otherwise this could cause misinterpretation at the consumer/producer side and lead to code injection/execution.

Document all supported content types in your API

Validate request content types

Reject requests containing unexpected or missing content type headers with HTTP response status 406 Unacceptable or 415 Unsupported Media Type

For XML content types ensure appropriate XML parser hardening, see the cheat sheet

Avoid accidentally exposing unintended content types by explicitly defining content types e.g. Jersey (Java) @consumes('application/json'); @produces('application/json'). This avoids XXE-attack vectors for example.

Send safe response content types

It is common for REST services to allow multiple response types (e.g. 'application/xml' or 'application/json', and the client specifies the preferred order of response types by the Accept header in the request.

Do NOT simply copy the Accept header to the Content-type header of the response.
Reject the request (ideally with a 406 Not Acceptable response) if the Accept header does not specifically contain one of the allowable types.

Services including script code (e.g. JavaScript) in their responses must be especially careful to defend against header injection attack.

ensure sending intended content type headers in your response matching your body content e.g. 'application/json' and not 'application/javascript'

Avoid exposing management endpoints via Internet.
If management endpoints must be accessible via the Internet, make sure that users must use a strong authentication mechanism, e.g. multi-factor.
Expose management endpoints via different HTTP ports or hosts preferably on a different NIC and restricted subnet.
Restrict access to these endpoints by firewall rules or use of access control lists.

Respond with generic error messages - avoid revealing details of the failure unnecessarily
Do not pass technical details (e.g. call stacks or other internal hints) to the client

Write audit logs before and after security related events
Consider logging token validation errors in order to detect attacks
Take care of log injection attacks by sanitising log data beforehand

To make sure the content of a given resources is interpreted correctly by the browser, the server should always send the Content-Type header with the correct Content-Type, and preferably the Content-Type header should include a charset. The server should also send an X-Content-Type-Options: nosniff to make sure the browser does not try to detect a different Content-Type than what is actually sent (can lead to XSS).

Additionally the client should send an X-Frame-Options: deny to protect against drag'n drop clickjacking attacks in older browsers.

CORS

Disable CORS headers if cross-domain calls are not supported
Be as specific as possible and as general as necessary when setting the origins of cross-domain calls

In Spring Boot (Java), for example, CORS support is disabled by default and is only enabled once the

The Cheat Sheet Jobs

endpoints.cors.allowed-origins property has been set. The configuration below permits GET and POST calls from the example.com domain:

endpoints.cors.allowed-origins=https://example.com

endpoints.cors.allowed-methods=GET,POST

In POST/PUT requests sensitive data should be transferred in the request body or request headers
In GET requests sensitive data should be transferred in an HTTP Header

OK:

https://example.com/resourceCollection/<id>/action
https://twitter.com/vanderaj/lists

NOT OK:

https://example.com/controller/<id>/action?apiKey=a53f435643de32 (API Key in URL)

HTTP defines status codes [1].When designing REST API, don't just use 200 for success or 404 for error. Always use the semantically appropriate status code for the response.

Here is a non-exhaustive selection of security related REST API status codes. Use it to ensure you return the correct code.

Status code	Message	Description
200	OK	Response to a successful REST API action. The HTTP method can be GET, POST, PUT, PATCH or DELETE
201	Created	The request has been fulfilled and resource created. A URI for the created resource is returned in the Location header
202	Accepted	The request has been accepted for processing, but processing is not yet complete
400	Bad Request	The request is malformed, such as message body format error
401	Unauthorized	Wrong or no authentication ID/password provided
403	Forbidden	It's used when the authentication succeeded but authenticated user doesn't have permission to the request resource
404	Not Found	When a non-existent resource is requested
406	Unacceptable	The client presented a content type in the Accept header which is not supported by the server API
405	Method Not Allowed	The error for an unexpected HTTP method. For example, the REST API is expecting HTTP GET, but HTTP PUT is used
413	Payload too large	Use it to signal that the request size exceeded the given limit e.g. regarding file uploads
415	Unsupported Media Type	The requested content type is not supported by the REST service
429	Too Many Requests	The error is used when there may be DOS attack detected or the request is rejected due to rate limiting
500	Internal Server Error	An unexpected condition prevented the server from fulfilling the request. Be aware that the response should not reveal internal information that helps an attacker, e.g. detailed error messages or stack traces.
501	Not Implemented	The REST service does not implement the requested operation yet
503	Service Unavailable	The REST service is temporarily unable to process the request. Used to inform the client it should retry at a later time.

Erlend Oftedal - erlend.oftedal@owasp.org
Andrew van der Stock - vanderaj@owasp.org
Tony Hsu Hsiang Chih- Hsiang_chihi@yahoo.com
Johan Peeters - yo@johanpeeters.com
Jan Wolff - jan.wolff@owasp.org
Rocco Gränitz - rocco.graenitz@owasp.org

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