CAPEC-245: XSS Using Doubled Characters

Description
The adversary bypasses input validation by using doubled characters in order to perform a cross-site scripting attack. Some filters fail to recognize dangerous sequences if they are preceded by repeated characters. For example, by doubling the < before a script command, (<<script or %3C%3script using URI encoding) the filters of some web applications may fail to recognize the presence of a script tag. If the targeted server is vulnerable to this type of bypass, the adversary can create a crafted URL or other trap to cause a victim to view a page on the targeted server where the malicious content is executed, as per a normal XSS attack.
Extended Description

Applications often need to transform data in and out of serialized data formats, such as XML and YAML, by using a data parser. It may be possible for an adversary to inject data that may have an adverse effect on the parser when it is being processed. By supplying oversized payloads in input vectors that will be processed by the parser, an adversary can cause the parser to consume more resources while processing, causing excessive memory consumption and CPU utilization, and potentially cause execution of arbitrary code. An adversary's goal is to leverage parser failure to their advantage. DoS is most closely associated with web services, SOAP, and Rest, because remote service requesters can post malicious data payloads to the service provider designed to exhaust the service provider's memory, CPU, and/or disk space. This attack exploits the loosely coupled nature of web services, where the service provider has little to no control over the service requester and any messages the service requester sends.

Severity :

Medium

Possibility :

Type :

Detailed
Relationships with other CAPECs

This table shows the other attack patterns and high level categories that are related to this attack pattern.

Prerequisites

This table shows the other attack patterns and high level categories that are related to this attack pattern.

  • The targeted web application does not fully normalize input before checking for prohibited syntax. In particular, it must fail to recognize prohibited methods preceded by certain sequences of repeated characters.
Skills required

This table shows the other attack patterns and high level categories that are related to this attack pattern.

Taxonomy mappings

Mappings to ATT&CK, OWASP and other frameworks.

Resources required

The adversary must trick the victim into following a crafted link to a vulnerable server or view a web post where the dangerous commands are executed.

Related CWE

A Related Weakness relationship associates a weakness with this attack pattern. Each association implies a weakness that must exist for a given attack to be successful.

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