| Attack Pattern ID | Pattern Abstraction: Standard 19 |
| Typical Severity | High |
| Description | Summary
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.
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| Attack Prerequisites |
Target software must be able to execute scripts, and also allow attacker to write/upload script
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| Typical Likelihood of Exploit |
High
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| Methods of Attack | |
| Examples-Instances | Description
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.
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| Attacker Skill or Knowledge Required |
Low → To load malicious script into open, e.g. world writable directory
Medium → Executing remote scripts on host and collecting output
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| Resources Required |
Ability to deploy a custom script on host
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| Solutions and Mitigations |
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: 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
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| Attack Motivation-Consequences | - Run Arbitrary Code
- Privilege Escalation
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| Context Description |
“Attack Pattern: Embedding Scripts within Scripts
The technology that runs the Internet is diverse and complex. There are hundreds of development languages, compilers, and interpreters that can build and execute code. Every developer has a sense for only part of the overall technology. Investments in time and money are made into each particular technology. As these systems evolve, the need to maintain backward compatibility becomes paramount. In management speak, this is the need to capitalize on an existing software investment. This is one reason that some newer scripting languages have backward support for older scripting languages.
As a result of this rapid and barely controlled evolution, much of the technology found in the wild can embed or otherwise access other languages and technologies in some form. This adds multiple layers of complexity and makes keeping track of all the disparate (yet available) functionality difficult at best. Filtering rules and security assumptions get swamped by the flow of new stuff. Looking for unanticipated functionality forgotten in the nooks and crannies of a system is an excellent technique."
[Hoglund and McGraw 04]
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| Injection Vector |
Malicious input delivered through standard script page, e.g. ASP web page
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| Payload |
Varies with instantiation of attack pattern. MAy contain network probe or attacks that run against or on host using host account permissions
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| Activation Zone |
Web server scripting host
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| Payload Activation Impact |
Enables attacker to execute scripts on remote host
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| Related Weaknesses | | CWE-ID | Weakness Name | Weakness Relationship Type |
|---|
| 79 | Failure to Sanitize Directives in a Web Page (aka 'Cross-site scripting' (XSS)) | Targeted | | 276 | Insecure Default Permissions | Targeted | | 279 | Insecure Execution-assigned Permissions | Secondary | | 284 | Access Control Issues | Secondary |
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| Related Attack Patterns | | ID | Name | Relationship Type | Relationship Description |
|---|
| 18 | Embedding Scripts in Nonscript Elements | Similar | |
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| Purpose | Penetration |
| CIA Impact | | Confidentiality Impact | Integrity Impact | Availability Impact |
|---|
| Medium | High | Low |
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| Technical Context | | Architectural Paradigm | Framework | Platform | Language |
|---|
| All | All | All | All |
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| References |
G. Hoglund and G. McGraw. Exploiting Software: How to Break Code. Addison-Wesley, February 2004.
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| Source | | Submission(s) |
|---|
| Submitter | Organization | Date | Comment |
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| G. Hoglund and G. McGraw. Exploiting Software: How to Break Code. Addison-Wesley, February 2004. | Cigital, Inc | 2007-01-01 | |
| Modification(s) |
|---|
| Modifier | Organization | Date | Comment |
|---|
| 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 |
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