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CAPEC-11: Cause Web Server Misclassification

 
Cause Web Server Misclassification
Definition in a New Window Definition in a New Window
Attack Pattern ID: 11
Abstraction: Standard
Status: Draft
Completeness: Complete
Presentation Filter:
+ Summary

An attack of this type exploits a Web server's decision to take action based on filename or file extension. Because different file types are handled by different server processes, misclassification may force the Web server to take unexpected action, or expected actions in an unexpected sequence. This may cause the server to exhaust resources, supply debug or system data to the attacker, or bind an attacker to a remote process.

This type of vulnerability has been found in many widely used servers including IIS, Lotus Domino, and Orion. The attacker's job in this case is straightforward, standard communication protocols and methods are used and are generally appended with malicious information at the tail end of an otherwise legitimate request. The attack payload varies, but it could be special characters like a period or simply appending a tag that has a special meaning for operations on the server side like .jsp for a java application server. The essence of this attack is that the attacker deceives the server into executing functionality based on the name of the request, i.e. login.jsp, not the contents.

+ Attack Execution Flow
Explore
  1. Footprint file input vectors:

    Manually or using an automated tool, an attacker searches for all input locations where a user has control over the filenames or MIME types of files submitted to the web server.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    Attacker manually crawls application to identify file inputs

    env-Web
    2

    Attacker uses an automated tool to crawl application identify file inputs

    env-Web
    3

    Attacker manually assesses strength of access control protecting native application files from user control

    env-Web
    4

    Attacker explores potential for submitting files directly to the web server via independently constructed HTTP Requests

    env-Web

    Indicators

    IDTypeIndicator DescriptionEnvironments
    1Positive

    Application submits files under user control to the web server

    env-Web
    2Negative

    Application does not submit files under user control to the web server

    env-Web
    3Negative

    Application strictly protects all native application files from user control

    env-Web

    Outcomes

    IDTypeOutcome Description
    1Success
    User-controllable files are identified
Experiment
  1. File misclassification shotgunning:

    An attacker makes changes to file extensions and MIME types typically processed by web servers and looks for abnormal behavior.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    Attacker submits files with switched extensions (e.g. .php on a .jsp file) to web server.

    env-Web
    2

    Attacker adds extra characters (e.g. adding an extra . after the file extension) to filenames of files submitted to web server.

    env-Web

    Indicators

    IDTypeIndicator DescriptionEnvironments
    1Positive

    The web server uses the wrong handler to execute the file, as expected by the attacker.

    env-Web
    2Inconclusive

    No result from the web server.

    env-Web
    3Negative

    The web server ignore the manipulation and process the request has it should have been.

    env-Web

    Outcomes

    IDTypeOutcome Description
    1Success
    Web server exhibits unexpected behavior.

    Security Controls

    IDTypeSecurity Control Description
    2Detective
    Monitor web server logs for excessive file processing errors
    3Preventative
    Always validate that file content structure matches implicitly or explicitly declared file type as first step of processing.
  2. File misclassification sniping:

    Understanding how certain file types are processed by web servers, an attacker crafts varying file payloads and modifies their file extension or MIME type to be that of the targeted type to see if the web server is vulnerable to misclassification of that type.

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    Craft a malicious file payload, modify file extension to the targeted file type and submit it to the web server.

    env-Web
    2

    Craft a malicious file payload, modify its associated MIME type to the targeted file type and submit it to the web server.

    env-Web

    Indicators

    IDTypeIndicator DescriptionEnvironments
    1Positive

    The web server uses the wrong handler to execute the file, as expected by the attacker.

    env-Web
    2Inconclusive

    No result from the web server.

    env-Web
    3Negative

    The web server ignore the manipulation and process the request has it should have been.

    env-Web

    Outcomes

    IDTypeOutcome Description
    1Success
    Attacker's payload is acted on by web server.
    2Failure
    The attacker cannot get the web server to misclassify a file.

    Security Controls

    IDTypeSecurity Control Description
    1Detective
    Monitor web server logs for excessive file processing errors
    2Preventative
    Always validate that file content structure matches implicitly or explicitly declared file type as first step of processing.
Exploit
  1. Disclose information:

    The attacker, by manipulating a file extension or MIME type is able to make the web server return raw information (not executed).

    Attack Step Techniques

    IDAttack Step Technique DescriptionEnvironments
    1

    Manipulate the file names that are explicitly sent to the server.

    env-Web
    2

    Manipulate the MIME sent in order to confuse the web server.

    env-Web

    Outcomes

    IDTypeOutcome Description
    1Success
    The attacker gets the information from the server

    Security Controls

    IDTypeSecurity Control Description
    1Preventative
    Always validate that file content structure matches implicitly or explicitly declared file type as first step of processing.
+ Attack Prerequisites
  • Web server software must rely on file name or file extension for processing.

+ Typical Severity

High

+ Typical Likelihood of Exploit

Likelihood: Medium

+ Methods of Attack
  • Injection
  • Modification of Resources
+ Examples-Instances

Description

J2EE application servers are supposed to execute Java Server Pages (JSP). There have been disclosure issues relating to Orion Application Server, where an attacker that appends either a period (.) or space characters to the end of a legitimate Http request, then the server displays the full source code in the attackers' web browser.

(Attack)
 
http://victim.site/login.jsp.

Since remote data and directory access may be accessed directly from the JSP, this is a potentially very serious issue.

[R.11.2]

+ Attacker Skills or Knowledge Required

Skill or Knowledge Level: Low

To modify file name or file extension

Skill or Knowledge Level: Medium

To use misclassification to force the Web server to disclose configuration information, source, or binary data

+ Resources Required

Ability to execute HTTP request to Web server

+ Solutions and Mitigations

Implementation: Server routines should be determined by content not determined by filename or file extension.

+ Attack Motivation-Consequences
ScopeTechnical ImpactNote
Confidentiality
Read memory
Read application data
Confidentiality
Access_Control
Authorization
Gain privileges / assume identity
+ Injection Vector

Malicious input delivered through standard Web application calls, e.g. HTTP Request.

+ Payload

Varies with instantiation of attack pattern. Malicious payload may alter or append filename or extension to communicate with processes in unexpected order.

+ Activation Zone

Client machine and client network

+ Payload Activation Impact

Enables attacker to force web server to disclose configuration, source, and data

+ Purposes
  • Reconnaissance
+ CIA Impact
Confidentiality Impact: HighIntegrity Impact: LowAvailability Impact: Low
+ Technical Context
Architectural Paradigms
All
Frameworks
All
Platforms
All
Languages
All
+ References
[R.11.1] [REF-2] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. February 2004.
[R.11.2] "Orion Application Server JSP Source Disclosure Vulnerability (Bugtraq ID: 17204)". SecurityFocus. Mar 23 2006. <http://www.securityfocus.com/bid/17204/info>.
+ Content History
Submissions
SubmitterOrganizationDateSource
CAPEC Content TeamThe MITRE Corporation2014-06-23Internal_CAPEC_Team
Modifications
ModifierOrganizationDateCommentsSource
CAPEC Content TeamThe MITRE Corporation2017-01-09Updated Related_Attack_PatternsInternal

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Page Last Updated or Reviewed: December 07, 2015