Embedding Scripts within Scripts |
| Attack Pattern ID: 19 (Standard Attack Pattern Completeness: Complete) | Typical Severity: High | Status: Draft |
DescriptionSummary
An attack of this type exploits a programs' vulnerabilities that are brought on by allowing remote hosts to execute scripts. The attacker leverages this capability to execute scripts to execute his/her own script by embedding it within other scripts that the target software is likely to execute. The attacker must have the ability to inject script into script that is likely to be executed. If this is done, then the attacker can potentially launch a variety of probes and attacks against the web server's local environment, in many cases the so-called DMZ, back end resources the web server can communicate with, and other hosts.
With the proliferation of intermediaries, such as Web App Firewalls, network devices, and even printers having JVMs and Web servers, there are many locales where an attacker can inject malicious scripts. Since this attack pattern defines scripts within scripts, there are likely privileges to execute said attack on the host.
Of course, these attacks are not solely limited to the server side, client side scripts like Ajax and client side Javascript can contain malicious scripts as well. In general all that is required is for there to be sufficient privileges to execute a script, but not protected against writing.
Attack Execution Flow
Spider:
Using a browser or an automated tool, an attacker records all entry points for inputs that happen to be reflected in a client-side script element. These script elements can be located in the HTML content (head, body, comments), in an HTML tag, XML, CSS, etc.
Attack Step Techniques
ID Attack Step Technique Description Environments 1 Use a spidering tool to follow and record all non static links that are likely to have input parameters (through forms, URL, fragments, etc.) actively used by the Web application.
env-Web2 Use a proxy tool to record all links visited during a manual traversal of the web application.
env-Web3 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.
env-WebIndicators
ID type Indicator Description Environments 1 Positive Inputs are used in a script element (script tag, DOM, etc.) and not in another type of element.
env-Web2 Inconclusive Using URL rewriting, parameters may be part of the URL path or the URL fragment.
env-Web3 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.
env-Web4 Negative Applications that have only static pages or that simply present information without accepting input are unlikely to be susceptible.
env-WebOutcomes
ID type Outcome Description 1 Success A list of URLs, with their corresponding parameters (POST, GET, COOKIE, etc.) is created by the attacker. These parameters are possibly used in client-side scripts elements.2 Success A list of application user interface entry fields is created by the attacker.3 Success A list of resources accessed by the application is created by the attacker.Security Controls
ID type Security Control Description 1 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).2 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.3 Preventative Use CAPTCHA to prevent the use of the application by an automated tool.4 Preventative Actively monitor the application and either deny or redirect requests from origins that appear to be automated.
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.
Attack Step Techniques
ID Attack Step Technique Description Environments 1 Manually inject various script payloads into each identified entry point using a list of common script injection probes that typically work in a client-side script elements context and observe system behavior to determine if script was executed.
env-Web2 Manually inject various script payloads into each identified entry point using a list of common script injection probes that typically work in a server-side script elements context and observe system behavior to determine if script was executed.
env-Web3 Use an automated injection attack tool to inject various script payloads into each identified entry point using a list of common script injection probes that typically work in a client-side script elements context and observe system behavior to determine if script was executed.
env-Web4 Use an automated injection attack tool to inject various script payloads into each identified entry point using a list of common script injection probes that typically work in a server-side script elements context and observe system behavior to determine if script was executed.
env-Web5 Use a proxy tool to record results of the created requests.
env-WebIndicators
ID type Indicator Description Environments 1 Positive User-controllable input is output back to the browser
env-Web2 Positive User-controllable input is embedded as part of script elements
env-Web3 Positive Output to the browser is not encoded to remove executable scripting syntax
env-Web4 Positive Server-side components execute script elements containing user-controllable input
env-WebOutcomes
ID type Outcome Description 1 Success The attacker's script string is being reflected 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, etc.)2 Success The attacker's script string is executed by the server-side component.3 Failure All context-sensitive characters are consistently re-encoded before being sent to the web browser.4 Inconclusive Some sensitive characters are consistently encoded, but others are not. Depending on which type of non-script element the payload is injected in, it may be possible to evade the encodings.Security Controls
ID type Security Control Description 1 Detective Monitor input to web servers (not only GET, but all potential inputs like COOKIES, POST, HEADER), 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 hackers use.2 Preventative Apply appropriate input validation to filter all user-controllable input of scripting syntax3 Preventative Do not embed user-controllable input in script elements.4 Preventative Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.
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.
Attack Step Techniques
ID Attack Step Technique Description Environments 1 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.
env-Web2 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.
env-WebOutcomes
ID type Outcome Description 1 Success The attacker gets the user's cookies or other session identifiers.2 Success The attacker gets the content of the page the user is viewing.3 Success The attacker causes the user's browser to visit a page with malicious content.Security Controls
ID type Security Control Description 1 Detective Monitor server logs for scripting parameters.2 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.3 Preventative Apply appropriate input validation to filter all user-controllable input of scripting syntax4 Preventative Appropriately encode all browser output to avoid scripting syntax5 Preventative Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.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).
Attack Step Techniques
ID Attack Step Technique Description Environments 1 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
env-Web2 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).
env-WebOutcomes
ID type Outcome Description 1 Success The attacker indirectly controls the user's browser and makes it performing actions exploiting CSRF.2 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.Security Controls
ID type Security Control Description 1 Detective Monitor server logs for scripting parameters.2 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.3 Preventative Apply appropriate input validation to filter all user-controllable input of scripting syntax4 Preventative Appropriately encode all browser output to avoid scripting syntax5 Preventative Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.Content spoofing:
By manipulating the content, the attacker targets the information that the user would like to get from the website.
Attack Step Techniques
ID Attack Step Technique Description Environments 1 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.
env-WebOutcomes
ID type Outcome Description 1 Success The user sees a page containing wrong informationSecurity Controls
ID type Security Control Description 1 Detective Monitor server logs for scripting parameters.2 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.3 Preventative Apply appropriate input validation to filter all user-controllable input of scripting syntax4 Preventative Appropriately encode all browser output to avoid scripting syntax5 Preventative Actively monitor the application and either deny or redirect requests from origins that appear to be generating XSS probes.
Attack PrerequisitesTarget software must be able to execute scripts, and also allow attacker to write/upload script
Typical Likelihood of ExploitLikelihood: High
Methods of Attack- Injection
- API Abuse
Examples-InstancesDescription
Ajax applications enable rich functionality for browser based web applications. Applications like Google Maps deliver unprecedented ability to zoom in and out, scroll graphics, and change grapic presentation through Ajax. The security issues that an attacker may exploit in this instance are the relative lack of security features in Javascript and the various browser's implementation of Javascript, these security gaps are what XSS and a host of other client side vulnerabilities are based on. While Ajax may not open up new security holes, per se, due to the conversational aspects between client and server of Ajax communication, attacks can be optimized. A single zoom in or zoom out on a graphic in an Ajax application may round trip to the server dozens of times. One of the first steps many attackers take is frequently footprinting an environment, this can include scanning local addresses like 192.*.*.* IP addresses, checking local directories, files, and settings for known vulnerabilities, and so on.
<IMG SRC=javascript:alert('XSS')>
The XSS script that is embeded in a given IMG tag can be manipulated to probe a different address on every click of the mouse or other motions that the Ajax application is aware of.
In addition the enumerations allow for the attacker to nest sequential logic in the attacks. While Ajax applications do not open up brand new attack vectors, the existing attack vectors are more than adequate to execute attacks, and now these attacks can be optimized to sequentially execute and enumerate host environments.
Attacker Skills or Knowledge RequiredSkill or Knowledge Level: Low
To load malicious script into open, e.g. world writable directory
Skill or Knowledge Level: Medium
Executing remote scripts on host and collecting output
Resources RequiredAbility to deploy a custom script on host
Solutions and MitigationsDesign: 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: Disable scripting languages such as Javascript in browser
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.
Implementation: Privileges are constrained, if a script is loaded, ensure system runs in chroot jail or other limited authority mode
Attack Motivation-Consequences- Run Arbitrary Code
- Privilege Escalation
Injection VectorMalicious input delivered through standard script page, e.g. ASP web page
PayloadVaries with instantiation of attack pattern. MAy contain network probe or attacks that run against or on host using host account permissions
Activation ZoneWeb server scripting host
Payload Activation ImpactEnables attacker to execute scripts on remote host
Related Weaknesses| CWE-ID | Weakness Name | Weakness Relationship Type |
|---|---|---|
| 79 | Failure to Preserve Web Page Structure ('Cross-site Scripting') | Targeted |
| 276 | Incorrect Default Permissions | Targeted |
| 279 | Incorrect Execution-Assigned Permissions | Secondary |
| 284 | Access Control (Authorization) Issues | Secondary |
| 692 | Incomplete Blacklist to Cross-Site Scripting | Targeted |
| 697 | Insufficient Comparison | Targeted |
| 713 | OWASP Top Ten 2007 Category A2 - Injection Flaws | Targeted |
| 71 | Apple '.DS_Store' | Targeted |
Related Attack Patterns| Nature | Type | ID | Name | Description | View(s) this relationship pertains to |
|---|---|---|---|---|---|
| PeerOf |  Attack Pattern | 18 | Embedding Scripts in Nonscript Elements | Mechanism of Attack1000 | |
| ChildOf | Attack Pattern | 242 | Script Injection | Mechanism of Attack (primary)1000 | |
| ChildOf |  Category | 341 | WASC Threat Classification 2.0 - WASC-08 - Cross-Site Scripting | WASC Threat Classification 2.0333 |
Purposes- Penetration
CIA Impact Technical Context| Architectural Paradigms | All |
|---|---|
| Frameworks | All |
| Platforms | All |
| Languages | All |
References Content History| Submissions | ||||
|---|---|---|---|---|
| Submitter | Organization | Date | ||
| G. Hoglund and G. McGraw. Exploiting Software: How to Break Code. Addison-Wesley, February 2004. | Cigital, Inc | 2007-01-01 | ||
| Modifications | |||||
|---|---|---|---|---|---|
| Modifier | Organization | Date | Comments | ||
| Gunnar Peterson | Cigital, Inc | 2007-02-28 | Fleshed out content to CAPEC schema from the original descriptions in "Exploiting Software" | ||
| Sean Barnum | Cigital, Inc | 2007-03-09 | Review and revise | ||
| Richard Struse | VOXEM, Inc | 2007-03-26 | Review and feedback leading to changes in ADescription and Related Attack Patterns | ||
| Sean Barnum | Cigital, Inc | 2007-04-13 | Modified pattern content according to review and feedback | ||
| Romain Gaucher | Cigital, Inc | 2009-02-10 | Created draft content for detailed description | ||
| Sean Barnum | Cigital Federal, Inc | 2009-04-13 | Reviewed and revised content for detailed description | ||
