Inappropriate Encoding for Output Context
|ID: 838||Date: (C)2012-05-14 (M)2012-11-08|
|Type: weakness||Status: INCOMPLETE|
|Abstraction Type: Base|
The software uses or specifies an encoding when generating
output to a downstream component, but the specified encoding is not the same as
the encoding that is expected by the downstream component.
Extended DescriptionThis weakness can cause the downstream component to use a decoding method
that produces different data than what the software intended to send. When
the wrong encoding is used - even if closely related - the downstream
component could decode the data incorrectly. This can have security
consequences when the provided boundaries between control and data are
inadvertently broken, because the resulting data could introduce control
characters or special elements that were not sent by the software. The
resulting data could then be used to bypass protection mechanisms such as
input validation, and enable injection attacks.While using output encoding is essential for ensuring that communications
between components are accurate, the use of the wrong encoding - even if
closely related - could cause the downstream component to misinterpret the
output.For example, HTML entity encoding is used for elements in the HTML body of
a web page. However, a programmer might use entity encoding when generating
output for that is used within an attribute of an HTML tag, which could
encoding.While web applications have received the most attention for this problem,
this weakness could potentially apply to any type of software that uses a
communications stream that could support multiple encodings.
Applicable PlatformsLanguage Class: Language-independent
Related Attack Patterns
|IntegrityConfidentialityAvailability ||Modify application
dataExecute unauthorized code or
commands ||An attacker could modify the structure of the message or data being
sent to the downstream component, possibly injecting commands. |
|Implementation ||Output Encoding ||Use context-aware encoding. That is, understand which encoding is
being used by the downstream component, and ensure that this encoding is
used. If an encoding can be specified, do so, instead of assuming that
the default encoding is the same as the default being assumed by the
downstream component. || || |
|Architecture and Design ||Output Encoding ||Where possible, use communications protocols or data formats that
provide strict boundaries between control and data. If this is not
feasible, ensure that the protocols or formats allow the communicating
components to explicitly state which encoding/decoding method is being
used. Some template frameworks provide built-in support. || || |
|Architecture and Design ||Libraries or Frameworks ||Use a vetted library or framework that does not allow this weakness to
occur or provides constructs that make this weakness easier to
avoid.For example, consider using the ESAPI Encoding control [R.838.7] or a
similar tool, library, or framework. These will help the programmer
encode outputs in a manner less prone to error.Note that some template mechanisms provide built-in support for the
appropriate encoding. || || |
|CWE-838 ChildOf CWE-845 ||Category ||CWE-844 || |
Demonstrative Examples (Details)
- This code dynamically builds an HTML page using POST data:
- CVE-2009-2814 : Server does not properly handle requests that do not contain UTF-8 data; browser assumes UTF-8, allowing XSS.
For more examples, refer to CVE relations in the bottom box.
White Box Definitions None
Black Box Definitions None
|CERT Java Secure Coding ||IDS12-J ||Perform lossless conversion of String data between differing
character encodings || |
|CERT Java Secure Coding ||IDS13-J ||Use compatible encodings on both sides of file or network
IO || |
- Jim Manico .Injection-safe templating languages. 2010-06-30.
- Dinis Cruz .Can we please stop saying that XSS is boring and easy to
- Ivan Ristic .Canoe: XSS prevention via context-aware output
- Jim Manico .What is the Future of Automated XSS Defense
- Jeremiah Grossman Robert "RSnake" Hansen Petko "pdp" D. Petkov Anton Rager Seth Fogie .XSS Attacks. Syngress. Section:'Preventing XSS Attacks'. Published on 2007.
- OWASP .DOM based XSS Prevention Cheat Sheet.
- OWASP .OWASP Enterprise Security API (ESAPI) Project.