Home > CAPEC List > CAPEC-111: JSON Hijacking (aka JavaScript Hijacking) (Version 2.11)  

CAPEC-111: JSON Hijacking (aka JavaScript Hijacking)

JSON Hijacking (aka JavaScript Hijacking)
Definition in a New Window Definition in a New Window
Attack Pattern ID: 111
Abstraction: Detailed
Status: Draft
Completeness: Complete
Presentation Filter:
+ Summary

An attacker targets a system that uses JavaScript Object Notation (JSON) as a transport mechanism between the client and the server (common in Web 2.0 systems using AJAX) to steal possibly confidential information transmitted from the server back to the client inside the JSON object by taking advantage of the loophole in the browser's Same Origin Policy that does not prohibit JavaScript from one website to be included and executed in the context of another website.

An attacker gets the victim to visit his or her malicious page that contains a script tag whose source points to the vulnerable system with a URL that requests a response from the server containing a JSON object with possibly confidential information. The malicious page also contains malicious code to capture the JSON object returned by the server before any other processing on it can take place, typically by overriding the JavaScript function used to create new objects. This hook allows the malicious code to get access to the creation of each object and transmit the possibly sensitive contents of the captured JSON object to the attackers' server.

There is nothing in the browser's security model to prevent the attackers' malicious JavaScript code (originating from attacker's domain) to set up an environment (as described above) to intercept a JSON object response (coming from the vulnerable target system's domain), read its contents and transmit to the attackers' controlled site. The same origin policy protects the domain object model (DOM), but not the JSON.

+ Attack Steps
  1. Understand How to Request JSON Responses from the Target System: An attacker first explores the target system to understand what URLs need to be provided to it in order to retrieve JSON objects that contain information of interest to the attacker.

    An attacker creates an account with the target system and observes requests and the corresponding JSON responses from the server. Understanding how to properly elicit responses from the server is crucial to the attackers' ability to craft the exploit.

  1. Craft a malicious website: The attacker crafts a malicious website to which he plans to lure the victim who is using the vulnerable target system. The malicious website does two things:

  1. Launch JSON hijack: An attacker lures the victim to the malicious website or leverages other means to get his malicious code executing in the victim's browser. Once that happens, the malicious code makes a request to the victim target system to retrieve a JSON object with sensitive information. The request includes the victim's session cookie if the victim is logged in.

    An attacker employs a myriad of standard techniques to get the victim to visit his or her malicious site or by some other means get the attackers' malicious code executing in the victim's browser.

+ Attack Prerequisites
  • JSON is used as a transport mechanism between the client and the server

  • The target server cannot differentiate real requests from forged requests

  • The JSON object returned from the server can be accessed by the attackers' malicious code via a script tag

+ Typical Severity


+ Typical Likelihood of Exploit

Likelihood: High

+ Methods of Attack
  • Protocol Manipulation
  • Analysis
  • Spoofing
+ Examples-Instances


Gmail service was found to be vulnerable to a JSON Hijacking attack that enabled an attacker to get the contents of the victim's address book. An attacker could send an e-mail to the victim's Gmail account (which ensures that the victim is logged in to Gmail when he or she receives it) with a link to the attackers' malicious site. If the victim clicked on the link, a request (containing the victim's authenticated session cookie) would be sent to the Gmail servers to fetch the victim's address book. This functionality is typically used by the Gmail service to get this data on the fly so that the user can be provided a list of contacts from which to choose the recipient of the e-mail.

When the JSON object with the contacts came back, it was loaded into the JavaScript space via a script tag on the attackers' malicious page. Since the JSON object was never assigned to a local variable (which would have prevented a script from a different domain accessing it due to the browser's same origin policy), another mechanism was needed to access the data that it contained. That mechanism was overwriting the internal array constructor with the attackers' own constructor in order to gain access to the JSON object's contents. These contents could then be transferred to the site controlled by the attacker.

+ Attacker Skills or Knowledge Required

Skill or Knowledge Level: Medium

Once this attack pattern is developed and understood, creating an exploit is not very complex.

The attacker needs to have knowledge of the URLs that need to be accessed on the target system to request the JSON objects.

+ Resources Required

None: No specialized resources are required to execute this type of attack.

+ Probing Techniques

Examine the typical asynchronous requests and responses between an AJAX client and the server to see how JSON objects are requested and what is returned.

+ Solutions and Mitigations

Ensure that server side code can differentiate between legitimate requests and forged requests. The solution is similar to protection against Cross Site Request Forger (CSRF), which is to use a hard to guess random nonce (that is unique to the victim's session with the server) that the attacker has no way of knowing (at least in the absence of other weaknesses). Each request from the client to the server should contain this nonce and the server should reject all requests that do not contain the nonce.

On the client side, the system's design could make it difficult to get access to the JSON object content via the script tag. Since the JSON object is never assigned locally to a variable, it cannot be readily modified by the attacker before being used by a script tag. For instance, if while(1) was added to the beginning of the JavaScript returned by the server, trying to access it with a script tag would result in an infinite loop. On the other hand, legitimate client side code can remove the while(1) statement after which the JavaScript can be evaluated. A similar result can be achieved by surrounding the returned JavaScript with comment tags, or using other similar techniques (e.g. wrapping the JavaScript with HTML tags).

Make the URLs in the system used to retrieve JSON objects unpredictable and unique for each user session.

Ensure that to the extent possible, no sensitive data is passed from the server to the client via JSON objects. JavaScript was never intended to play that role, hence the same origin policy does not adequate address this scenario.

+ Attack Motivation-Consequences
ScopeTechnical ImpactNote
Read application data
+ Relevant Security Requirements

Ensure that a mechanism is in place for the server side code to differentiate between legitimate requests and forged requests

On the client side, ensure that the returned JavaScript from the server can only be evaluated locally after being assigned to a variable and not via a script tag

Ensure that URLs used to request server responses that pass the JSON objects back to the client are hard to guess and are unique per user session

+ Purposes
  • Exploitation
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: LowAvailability Impact: Low
+ Technical Context
Architectural Paradigms
+ Content History
CAPEC Content TeamThe MITRE Corporation2014-06-23Internal_CAPEC_Team
CAPEC Content TeamThe MITRE Corporation2015-12-07Updated Related_Attack_PatternsInternal
CAPEC Content TeamThe MITRE Corporation2017-08-04Updated Attacker_Skills_or_Knowledge_Required, Resources_RequiredInternal

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Page Last Updated or Reviewed: July 31, 2017