CIS14: Best Practices You Must Apply to Secure Your APIs

Best Prac*ces You Must Apply to Secure Your APIs

K. Sco7 Morrison SVP and Dis+nguished Engineer

© 2014 CA. ALL RIGHTS RESERVED.

Here Is What This Talk Is About:

§  The new API threat –  …and the poten+al rise of the hacker-‐robber-‐baron

§  Are APIs just like the Web? Or are they different? –  Look at three important areas:

1.  Parameteriza+on 2.  Iden+ty 3.  Cryptography

§  How to apply the lessons of this talk


What is an API?

Web App

API Server

Web Client

Mobile App

An API is a RESTful service


For Example:

GET http://services.layer7.com/staff/Scott


For Example:

{ "firstName": ”Sco ̂ ", "lastName" : ”Morrison", ”+tle" : “CTO”, "address" : { "streetAddress": ”405-‐1100 Melville", "city" : ”Vancouver", ”prov" : ”BC", "postalCode" : ”V6E 4A6" }, "phoneNumber": [ { "type" : ”office", "number": ”605 681-‐9377" }, { "type" : ”home", "number": ”604 555-‐4567" } ] }

http://services.layer7.com/staff/Scott


“Sounds great. So what’s the problem?”

API Development != Web Development

In Par*cular: We need to be wary of bad web development prac=ces migra=ng

to APIs…


Problem Area #1: API Parameteriza=on

§  In the tradi+onal web world, parameteriza+on was limited and indirect –  Subject to the capabili+es of URLs and forms

§  APIs in contrast and offer much more explicit parameteriza+on –  The full power of RESTful design: GET, POST, PUT, DELETE

§  (And don’t stop there… what about effects of HEAD, etc)?

§  This creates a greater poten+al aâck surface –  Injec+on, bounds, correla+on, and so on


Good Web Apps Constrain

HTTP Server

App Server

Database

Web Client

Objects

Pages

Constraint Space

Records


APIs Are A More Direct Conduit

HTTP Server

App Server

Database

App

Objects

OIen: •  Self-‐documen+ng •  Closely mapped to object space,

data structure, etc

APIs can leak informa*on


APIs Also Increase A7ack Surface


Aâcker

Web App Server (browser+APIs)

Vic+m: Web Browser Client

<SCRIPT …> 1. API injects script in

3. Browser loads content with

embedded script

2. Server fails to perform FIEO: Filter Input, Escape Output

API

Script Inser*on is Just One Poten*al Exploit


SQL Injec+on is Another

Source: h^ps://xkcd.com/327/

Exploits of a Mom


Mi*ga*on Strategy

§  Rigorous valida+on of consumer supplied inputs – and API output! –  Stronger typing –  Sets and ranges –  Avoid auto-‐generated schemas that make everything a string

§  Use schema valida+on –  XML Schema, RELAX-‐NG, Schematron – Pick your poison

§  Please no DTDs! –  JSON schema valida+on –  Return of IDLs: WADL, RAML, Swagger, etc

Constrain by Default


Mi*ga*on Strategy (cont.)

§  Regex scanning for signatures §  Tune paêrns for the API

–  Some+mes SELECT is OK

§  Virus scanning of aâchments –  Don’t forget B64’d message content

§  Library, service, or gateway solu+ons –  Decoupled security –  What are the tradeoffs?


Mi*ga*on Strategy (cont.)

§  Whitelist tags if you can (i.e. where the valida+on space is small and concise) –  Not always prac+cal –  (Note that I’m referring to whitelis+ng tags not IPs.)

§  Blacklist dangerous tags like <SCRIPT> §  Always perform FIEO (Filter Input, Escape Output)

§  Watch for fuzzing –  This is a trend—not an event!

§  Learn more: h^p://xssed.com


Problem Area #2: Iden=ty

§  We had it surprisingly good in the Web world –  Browser session usually +ed to human –  Dealing with one iden+ty is not so tough

§  Security tokens abound, but solu+ons are mature –  Username/pass, x.509 certs, mul+-‐factor, Kerberos, SAML, etc

–  APIs rapidly becoming more difficult §  Non-‐human en++es §  Mul+ple layers of relevant iden++es

–  Me, my a^ributes, my phone, my developer, my provider…


API Keys

“An applica*on programing interface key (API key) is a code generated by websites that allow users to access their

applica+on programming interface. API keys are used to track how the API is being used in order to prevent malicious use or

abuse of the terms of service.

API keys are based on the UUID system to ensure they will be unique to each user.”

(Source: wikipedia h^p://en.wikipedia.org/wiki/Applica+on_programming_interface_key )


For Example:

GET http://example.layer7.com/services/staff

?APIKey=15458617-‐7813-‐4a37-‐94ac-‐a8e6da6f6405

Seriously? WTF.


How Does An API Key Map To Iden+ty?

15458617-‐7813-‐4a37-‐94ac-‐a8e6da6f6405

A

A person?

Or an app?

It is en+rely inconsistent


The Iden+ty Profile

Increasingly we need to move toward large number of claims (mul+ple iden+ty profile)

•  appID •  userID •  deviceID

•  User attributes •  Roles •  Geo location •  IP •  User agent •  Time of day •  etc


Where Did API Keys Come From?

§  API keys came from Google APIs like maps, early Yahoo APIs, early Twiêr APIs etc. –  Originally meant for loose, non-‐authorita+ve tracking –  Rate limits, approximate usage profiling

§  Google geocoding v3.0 API deprecates API keys –  Uses IP instead to track and thro^le –  This has its own set of problems

§  IP address spoofing §  Problems with legi+mate clients like cloud servers

§  Google Premier used a public client_id and requires signed URLs –  (Strips domain leaving only path and query parameters)


Boôm Line: The API Key Was Never Meant To Be Authorita+ve

§  Strange hybrid of HTTP’s USER-‐AGENT and session con+nuity

§  OK only for general tracking §  Anything that maêrs should use real security tokens

– Anywhere where iden+ty is important: §  APIs that provide access to sensi+ve data §  APIs that change things that maêr §  APIs that charge for use §  etc.


Move to OAuth For People


Mi+ga+on

§  Protect the tokens! §  HTTPS everywhere

–  This is another web design cultural issue –  It’s just not that expensive any more

§  OAuth for people §  APIKeys for apps

–  Assume this is non-‐authorita+ve

§  Consider behavioral iden+fica+on of apps –  Apps are rigid in their API flow

Important!


Problem Area #3: Cryptography and PKI

§  Cryptography is reasonably mature on the web –  Surprisingly limited use paêrns –  SSL/TLS –  Very li^le tough PKI (like client-‐side)

§  So what’s wrong with APIs?


It’s Like We Forgot Everything We Knew

§  Emailing keys –  API, shared secrets, etc.

§  Bad storage schemes –  Security through obscurity –  Toy ciphers

§  No life cycle management –  Limits on use –  Time limits –  Revoca+on –  Audit


The Issues

§  Key management –  Especially across farms

§  Nobody takes web PKI seriously –  CRLs and OCSP aren’t much good in the browser world

§  Fail open—seriously

§  CA trust breakdown –  Indian NIC issue July 2014

§  Subordinate CA issued fraudulent Google and Yahoo certs


The Issues (cont.)

§  Cipher suite restric+ons –  Avoiding downgrades

§  Client-‐side cer+ficate authen+ca+on is hard §  The alterna+ves for parameter confiden+ality and/or integrity

are hard: –  XML encryp+on is s+ll there

§  Not for the faint of heart –  OAuth 1.0 gave you parameter signing

§  Only op+onal in 2.0 –  JWT signing and encryp+on emerging


SSL Everywhere

(it’s cheap)


Mi+ga+ons

§  SSL everywhere §  Use real PKI

–  I know it’s painful

§  Use HSMs to protect keys that really maêr

§  Otherwise use real key material protec+on schemes –  PKCS #12, etc –  Libraries abound

§  You must do CRLs and OCSP for APIs


Where Does This All Leave Us?

§  SOAP, the WS-‐* stack dealt with much of this very rigorously –  But it was just too hard.

§  We need to learn from this, but make it easier to implement

§  Here’s how…


How Do I Apply This Today?

§  Use SSL for all API transac+ons –  Hides many sins

§  Confiden+ality, integrity, replay, binding token+message, server authen+ca+on, etc.

§  Use real PKI –  Yes, it’s hard –  But you can’t skimp here

§  Use OAuth for distributed authen+ca+on §  Validate all data going in and out of an API §  Use real frameworks, don’t reinvent

SVP and Dis+nguished Engineer

Sco^[email protected]

@KSco^Morrison

h^p://KSco^Morrison.com

linkedin.com/KSco^Morrison

ca.com

K. Sco7 Morrison

Technology

CIS14: Best Practices You Must Apply to Secure Your APIs