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MOHAMMED A. IMRANRESTful Web ServicesPentesting
Hello
MOHAMMED A. IMRANApplication Security Engineer, CA IncNull Hyderabad LeadOWASP Hyderabad Board Member
@MohammedAImran
MICreated and Designed using
LET’S TALK ABOUT ...
P RO B L E M S W I T H R E S TW S T E S T I N G
TO O L S & T E C H N I Q U E S
W H AT I S R E S Tfu l W E B S E RV I C E S ?
M E T H O D O LO G Y TO T E S TR E S Tfu l W S
DIDYOUKNOW?
THE
UGLY
TRU
TH SOAP Webservices VS RESTful Webservices
Google Trends
They also rest on REST APIs
Why REST WebServices ?
Easy & Simple
<?xml version="1.0"?><soap:Envelopexmlns:soap="http://www.w3.org/2001/12/soap-envelope"soap:encodingStyle="http://www.w3.org/2001/12/soap-encoding">
<soap:Body xmlns:m="http://www.mysite.com/users"> <m:GetUserDetails> <m:UserID>313</m:UserID> </m:GetUserDetails></soap:Body>
</soap:Envelope>
GET /users/313/
VS
Light weight<soap:Body xmlns:m="http://www.mysite.com/users"> <m:GetUserDetailsResponse> <m:UserName>MohammedAImran</m:UserName>
<m:Type>user</m:Type>
<m:SiteAdmin>false</m:SiteAdmin>
<m:UserName>Mohammed A.Imran</m:UserName>
<m:Company>CA Inc</m:Company>
<m:Email> [email protected] </m:Email> </m:GetUserDetailsResponse></soap:Body>
{ "login": "MohammedAImran", "type": "User", "site_admin": false, "name": "Mohammed A. Imran", "company": "CA Inc", "email": "[email protected]" }
VS
Note: REST can also use XML as media type
Many more reasons to use ...● Easy to understand & document● Easy on limited bandwidth● READS can be cached and hence reduces the bandwidth● Better browser support since data format mostly is json● Can be used by mobile devices● Loosely coupled
But what is REST ?
Representational state transfer (REST) is an architectural style consisting of a coordinated set of constraints applied to components, connectors, and data elements, within a distributed hypermedia system.
“”
What ? Let me explain ...
REST is an architectural style with some imposed constraints in how data is accessed and represented while developing web services or applications. It uses HTTP 1.1 as inspiration.
In simple terms
REST = RFC 2616 Well, almost
In simple terms ...
REST = HTTP Protocol
with constraints
Architecture constraints● Uniform interface● Client-server● Stateless● Cache-able● Layered system● Code on demand(optional)
REST Style consists of ...
Resources VERBS Media Types Status Codes
REST Style consists of ...
Resource URLs VERBS Media Types Status Codes
RESOURCES
Site.com/users/1
INSTANCE RESOURCES
CollectionRESOURCES
NOUN
Site.com/users
REST Style consists of ...
Resources VERBS Media Types Status Codes
VERBS
POST
READ
PUT
DELETE
POST = CREATECreate a new some resource
*
* POST can be used for both create and update
POST http://mysite.com/users/
{ "login": "MohammedAImran", "id": "313", "name": "Mohammed A. Imran", "company": "CA Inc", "email": "[email protected]"}
GET = READFetch some resource
GET site.com/users/
{ users:[ { "login": "MohammedAImran", "id": "313", "name": "Mohammed A. Imran", "company": "CA Inc", "email": "[email protected]"}, { "login": "Raghunath", "id": "311", "name": " G Raghunath", "company": "X Inc", "email": "[email protected]"}]}
GET site.com/users/313 { "login": "MohammedAImran", "id": "313", "name": "Mohammed A. Imran", "company": "CA Inc", "email": "[email protected]"}
PUT =UPDATE/MODIFYUpdate some resource
* PUT can be used for both create and update
*
DELETE = DELETEDelete a resource
REST Style consists of ...
Resources VERBS Media Types Status Codes
HATEOAS
Hypermedia As The Engine Of Application State
Media TypesParsing RulesSpecifications
+ =
Media Type ExamplesApplication/json
Application/xml
Application/imrans+json;v1
REST Style consists of ...
Resources VERBS Media Types Status Codes
Status Codes
400 Bad Request 401 Unauthorized 403 Forbidden 404 Not Found 405 Method Not Allowed 409 Conflict
200 OK201 Created204 No Content304 Not Modified500 Internal Server Error501 Not Implemented
RESTful WS testing problems
Difficulty in doing REST PT● Many JSON variables to fuzz and difficult to find which ones
are optional and to be fuzzed● Custom authentication● Statelessness● Non common HTTP status codes which tools are used to
Difficulty in doing REST PT ...● Not so good automated tool support● Every API is different from other and hence need custom
tweaking for tools● Heavy reliance on Ajax frameworks for creating PUT and
DELETE requests as most browsers don’t support them
REST WS testing Methodology
Authentication
Bad practices
http://site.com/token/a3b3c2be5f53c8/
https://site.com/token/a3b3c2be5f53c8/
Authentication ...● REST APIs rely heavily on SSL● Often basic authentication is coupled with SSL ( Bruteforce ? )● Often custom token authentication schemes are built and used
( a sure recipe for disaster) ● Never pass username/password, tokens, keys in URL
(use POST instead )● Implementing authentication tokens in Headers takes away headache of
having a CSRF token
Session Management● Check all session based attacks on tokens as well● Session timeout● Session brute force● Generally tokens are stored in local storage of browsers,
make sure you delete the token after log-out and upon browser window close
● Invalidate the token at server side upon on logout
Authorization● Privilege escalation (Horizontal and Vertical)● Make sure there is a tight access control on DELETE, PUT methods● Use role based authentication● Since usually the consumers of the REST APIs are machines, there
are no checks if service is heavily used, could lead to DoS or BruteForce.
● Protect administrative functionality
CVE-2010-0738
JBOSS JMX Console Vulnerability
NOTE
All attacks which are possible on any web application are possible with REST APIs as well.
Input Validation● SQL Injection● XSS● Command Injection● XPATH Injection
However XSS becomes difficult to fuzz because of JSON and you might want to scan with sql injection and xss profiles separately
Output encoding● If you application has a web interface then might want to use
the following headers:– X-Content-Type-Options: nosniff– X-Frame-Options: DENY/SAMEORIGIN/ALLOW-FROM
● JSON Encoding
Cryptography● Use TLS with good key size (384 bits preferably)● Use client side certificates possible however not usually seen
for APIs● Use strong hashing algorithms(scrypt/bcrypt/SHA512)● Use strong encryption mechanisms (AES)
Few notes ...● Use proxy to determine the attack surface and to understand
the application● Identify URLs, Resources, status codes and data needed● Every part of the http protocol is potential for fuzzing in
RESTful APIs (dont forget headers)● WAF evasion is possible since json is not well understood by
WAFs
Tools & Techniques
Command-line-Fu
cURL Primer cURL
-b or - -cookie ”COOKIE HERE”
-h or - -header “Authorization: Custom SW1yYW5XYXNIZXJlCg==”
-X or - -request PUT/POST/DELETE
-i or - -include //include response headers
-d or - -data “username=imran&password=Imran” or - -data @filecontaining-data
-x or - - proxy 127.0.0.1:8080
-A or - -user-agent ”Firefox 27.0”
cURL Primer ...● cURL is great for automation if you know how service works.● cURL libraries are available for majority of the languages like php, python
and many more...● You can perform complex operations and script them pretty fast.
cURL Examples #!/bin/bash
users="Imran Jaya Raghu Vinayak"
for dirName in $users
do
curl -i -H “Authorization: Custom SW1yYW5XYXNIZXJlCg==” "http://www.mysite.com/users/$dirName" --proxy 127.0.0.1:8080
done
Graphical Tools
Firefox Add-on
Firefox Add-on ...● If you need graphical interface, browser add-ons provide GUI, however not
as powerful as the cURL command.● Specialized developer tools ( SOAP UI ) can also be used for testing.
Automated Tools
AppScan Scan
http://blog.watchfire.com/wfblog/2012/01/testing-restful-services-with-appscan-standard.html
AppScan Scan...
Thank you !
Want to discuss more ? Catch me on
www.twitter.com/MohammedAImran www.linkedin.com/in/MohammedAImran
You might like these as well!
Credits
* All icons are taken from The Noun project, credit goes to respective artists
* OWASP Cheat sheet series
Referenceshttp://www.slideshare.net/SOURCEConference/security-testing-for-rest-applications-ofer-shezaf-source-barcelona-nov-2011
https://www.owasp.org/index.php/REST_Security_Cheat_Sheet
http://securityreliks.wordpress.com/2010/07/28/testing-restful-services-with-appscan/
http://www-01.ibm.com/support/docview.wss?uid=swg21412832
http://blog.watchfire.com/wfblog/2012/01/testing-restful-services-with-appscan-standard.html
