CAPEC-63 - Simple Script Injection

An attacker embeds malicious scripts in content that will be served to web browsers. The goal of the attack is for the target software, the client-side browser, to execute the script with the users' privilege level.

An attack of this type exploits a programs' vulnerabilities that are brought on by allowing remote hosts to execute code and scripts. Web browsers, for example, have some simple security controls in place, but if a remote attacker is allowed to execute scripts (through injecting them in to user-generated content like bulletin boards) then these controls may be bypassed. Further, these attacks are very difficult for an end user to detect.

Severity

Likelihood

Confidentiality

Integrity

Availability

  • Attack Methods 3
  • Injection
  • Modification of Resources
  • Protocol Manipulation
  • Purposes 2
  • Penetration
  • Exploitation
  • Scopes 3
  • Execute unauthorized code or commands
  • Availability
  • Integrity
  • Confidentiality
  • Modify application data
  • Integrity
  • Read application data
  • Confidentiality

Low level: To achieve a redirection and use of less trusted source, an attacker can simply place a script in bulletin board, blog, wiki, or other user-generated content site that are echoed back to other client machines.

High level: Exploiting a client side vulnerability to inject malicious scripts into the browser's executable process.

Target client software must be a client that allows scripting communication from remote hosts, such as a JavaScript-enabled Web Browser

Ability to deploy a custom hostile service for access by targeted clients. Ability to communicate synchronously or asynchronously with client machine

Step 1 - Survey the application for user-controllable inputs

Using a browser or an automated tool, an attacker follows all public links and actions on a web site. He records all the links, the forms, the resources accessed and all other potential entry-points for the web application..

Tecnique ID: 1 - Environment(s) env-Web

Use a spidering tool to follow and record all links and analyze the web pages to find entry points. Make special note of any links that include parameters in the URL.

Tecnique ID: 2 - Environment(s) env-Web

Use a proxy tool to record all links visited during a manual traversal of the web application.

Tecnique ID: 3 - Environment(s) env-Web

Use a browser to manually explore the website and analyze how it is constructed. Many browsers' plugins are available to facilitate the analysis or automate the discovery.

Indicator ID: 1 - Environment(s) env-Web

Type: Positive

Inputs are used by the application or the browser (DOM)

Indicator ID: 2 - Environment(s) env-Web

Type: Inconclusive

Using URL rewriting, parameters may be part of the URL path.

Indicator ID: 3 - Environment(s) env-Web

Type: Inconclusive

No parameters appear to be used on the current page. Even though none appear, the web application may still use them if they are provided.

Indicator ID: 4 - Environment(s) env-Web

Type: Negative

Applications that have only static pages or that simply present information without accepting input are unlikely to be susceptible.


Security Control ID: 1

Type: Detective

Monitor velocity of page fetching in web logs. Humans who view a page and select a link from it will click far slower and far less regularly than tools. Tools make requests very quickly and the requests are typically spaced apart regularly (e.g. 0.8 seconds between them).

Security Control ID: 2

Type: Detective

Create links on some pages that are visually hidden from web browsers. Using iframes, images, or other HTML techniques, the links can be hidden from web browsing humans, but visible to spiders and programs. A request for the page, then, becomes a good predictor of an automated tool probing the application.

Security Control ID: 3

Type: Preventative

Use CAPTCHA to prevent the use of the application by an automated tool.

Security Control ID: 4

Type: Preventative

Actively monitor the application and either deny or redirect requests from origins that appear to be automated.


Outcome ID: 1

Type: Success

A list of URLs, with their corresponding parameters (POST, GET, COOKIE, etc.) is created by the attacker.

Outcome ID: 2

Type: Success

A list of application user interface entry fields is created by the attacker.

Outcome ID: 3

Type: Success

A list of resources accessed by the application is created by the attacker.



Step 1 - Probe identified potential entry points for XSS vulnerability

The attacker uses the entry points gathered in the "Explore" phase as a target list and injects various common script payloads to determine if an entry point actually represents a vulnerability and to characterize the extent to which the vulnerability can be exploited..

Tecnique ID: 1 - Environment(s) env-Web

Use a list of XSS probe strings to inject script in parameters of known URLs. If possible, the probe strings contain a unique identifier.

Tecnique ID: 2 - Environment(s) env-Web

Use a proxy tool to record results of manual input of XSS probes in known URLs.

Tecnique ID: 3 - Environment(s) env-Web

Use a list of XSS probe strings to inject script into UI entry fields. If possible, the probe strings contain a unique identifier.

Tecnique ID: 4 - Environment(s) env-Web

Use a list of XSS probe strings to inject script into resources accessed by the application. If possible, the probe strings contain a unique identifier.

Indicator ID: 1 - Environment(s) env-Web

Type: Positive

The output of pages includes some form of a URL parameter. e.g., ?error="'(){};=" becomes "'(){}=" in the title of the web page.

Indicator ID: 2 - Environment(s) env-Web

Type: Positive

Input content becomes part of the web page.

Indicator ID: 3 - Environment(s) env-Web

Type: Inconclusive

Nothing is returned to the web page. It may be a stored XSS. The unique identifier from the probe helps to trace the flow of the possible XSS.


Security Control ID: 1

Type: Detective

Monitor input to web servers (not only GET, but all potential inputs), application servers, and other HTTP infrastructure (e.g., load balancers). Alert on standard XSS probes. The majority of attackers use well-known strings to check for vulnerabilities. Use the same vulnerability catalogs that adversaries use.

Security Control ID: 2

Type: Preventative

Apply appropriate input validation to filter all user-controllable input of scripting syntax

Security Control ID: 3

Type: Preventative

Appropriately encode all browser output to avoid scripting syntax

Security Control ID: 4

Type: Preventative

Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.


Outcome ID: 1

Type: Success

The attacker's cross-site scripting string is repeated back verbatim at some point in the web site (if not on the same page). Note that sometimes, the payload might be well encoded in the page, but wouldn't be encoded at all in some other section of the same web page (title, script, etc.)

Outcome ID: 2

Type: Failure

All HTML-sensitive characters are consistently re-encoded before being sent to the web browser.

Outcome ID: 3

Type: Inconclusive

Some sensitive characters are consistently encoded, but others are not.



Step 1 - Steal session IDs, credentials, page content, etc.

As the attacker succeeds in exploiting the vulnerability, he can choose to steal user's credentials in order to reuse or to analyze them later on..

Tecnique ID: 1 - Environment(s) env-Web

Develop malicious JavaScript that is injected through vectors identified during the Experiment Phase and loaded by the victim's browser and sends document information to the attacker.

Tecnique ID: 2 - Environment(s) env-Web

Develop malicious JavaScript that injected through vectors identified during the Experiment Phase and takes commands from an attacker's server and then causes the browser to execute appropriately.

Security Control ID: 1

Type: Detective

Monitor server logs for scripting parameters.

Security Control ID: 2

Type: Detective

Monitor server logs for referrers. If users are being tricked into clicking XSS links through forums or other web postings, their web browsers will be providing Referrer headers most of the time. These can help indicate that the actual request is illegitimate.

Security Control ID: 3

Type: Preventative

Apply appropriate input validation to filter all user-controllable input of scripting syntax

Security Control ID: 4

Type: Preventative

Appropriately encode all browser output to avoid scripting syntax

Security Control ID: 5

Type: Preventative

Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.


Outcome ID: 1

Type: Success

The attacker gets the user's cookies or other session identifiers.

Outcome ID: 2

Type: Success

The attacker gets the content of the page the user is viewing.

Outcome ID: 3

Type: Success

The attacker causes the user's browser to visit a page with malicious content.


Step 2 - Forceful browsing

When the attacker targets the current application or another one (through CSRF vulnerabilities), the user will then be the one who perform the attacks without being aware of it. These attacks are mostly targeting application logic flaws, but it can also be used to create a widespread attack against a particular website on the user's current network (Internet or not)..

Tecnique ID: 1 - Environment(s) env-Web

Develop malicious JavaScript that is injected through vectors identified during the Experiment Phase and loaded by the victim's browser and performs actions on the same web site

Tecnique ID: 2 - Environment(s) env-Web

Develop malicious JavaScript that injected through vectors identified during the Experiment Phase and takes commands from an attacker's server and then causes the browser to execute request to other web sites (especially the web applications that have CSRF vulnerabilities).

Security Control ID: 1

Type: Detective

Monitor server logs for scripting parameters.

Security Control ID: 2

Type: Detective

Monitor server logs for referrers. If users are being tricked into clicking XSS links through forums or other web postings, their web browsers will be providing Referrer headers most of the time. These can help indicate that the actual request is illegitimate.

Security Control ID: 3

Type: Preventative

Apply appropriate input validation to filter all user-controllable input of scripting syntax

Security Control ID: 4

Type: Preventative

Appropriately encode all browser output to avoid scripting syntax

Security Control ID: 5

Type: Preventative

Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.


Outcome ID: 1

Type: Success

The attacker indirectly controls the user's browser and makes it performing actions exploiting CSRF.

Outcome ID: 2

Type: Success

The attacker manipulates the browser through the steps that he designed in his attack. The user, identified on a website, is now performing actions he is not aware of.


Step 3 - Content spoofing

By manipulating the content, the attacker targets the information that the user would like to get from the website..

Tecnique ID: 1 - Environment(s) env-Web

Develop malicious JavaScript that is injected through vectors identified during the Experiment Phase and loaded by the victim's browser and exposes attacker-modified invalid information to the user on the current web page.

Security Control ID: 1

Type: Detective

Monitor server logs for scripting parameters.

Security Control ID: 2

Type: Detective

Monitor server logs for referrers. If users are being tricked into clicking XSS links through forums or other web postings, their web browsers will be providing Referrer headers most of the time. These can help indicate that the actual request is illegitimate.

Security Control ID: 3

Type: Preventative

Apply appropriate input validation to filter all user-controllable input of scripting syntax

Security Control ID: 4

Type: Preventative

Appropriately encode all browser output to avoid scripting syntax

Security Control ID: 5

Type: Preventative

Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.


Outcome ID: 1

Type: Success

The user sees a page containing wrong information



Design: Use browser technologies that do not allow client side scripting.

Design: Utilize strict type, character, and encoding enforcement

Design: Server side developers should not proxy content via XHR or other means, if a http proxy for remote content is setup on the server side, the client's browser has no way of discerning where the data is originating from.

Implementation: Ensure all content that is delivered to client is sanitized against an acceptable content specification.

Implementation: Perform input validation for all remote content.

Implementation: Perform output validation for all remote content.

Implementation: Session tokens for specific host

Implementation: Patching software. There are many attack vectors for XSS on the client side and the server side. Many vulnerabilities are fixed in service packs for browser, web servers, and plug in technologies, staying current on patch release that deal with XSS countermeasures mitigates this.