Description

The software prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

Extended Description

Improper encoding or escaping can allow attackers to change the commands that are sent to another component, inserting malicious commands instead.

Most software follows a certain protocol that uses structured messages for communication between components, such as queries or commands. These structured messages can contain raw data interspersed with metadata or control information. For example, "GET /index.html HTTP/1.1" is a structured message containing a command ("GET") with a single argument ("/index.html") and metadata about which protocol version is being used ("HTTP/1.1").

If an application uses attacker-supplied inputs to construct a structured message without properly encoding or escaping, then the attacker could insert special characters that will cause the data to be interpreted as control information or metadata. Consequently, the component that receives the output will perform the wrong operations, or otherwise interpret the data incorrectly.

Likelihood of Exploit: Very High

Applicable Platforms
Language Class: All
Technology Class: Often
Technology Class: Database-Server
Technology Class: Often
Technology Class: Web-Server

Time Of Introduction

• Architecture and Design
• Implementation
• Operation

Related Attack Patterns

• CAPEC-104
• CAPEC-18
• CAPEC-63
• CAPEC-73
• CAPEC-81
• CAPEC-85
• CAPEC-86

Common Consequences

Detection Methods

Potential Mitigations

Relationships
This weakness is primary to all weaknesses related to injection (CWE-74) since the inherent nature of injection involves the violation of structured messages.
CWE-116 and CWE-20 have a close association because, depending on the nature of the structured message, proper input validation can indirectly prevent special characters from changing the meaning of a structured message. For example, by validating that a numeric ID field should only contain the 0-9 characters, the programmer effectively prevents injection attacks.
However, input validation is not always sufficient, especially when less stringent data types must be supported, such as free-form text. Consider a SQL injection scenario in which a last name is inserted into a query. The name "O'Reilly" would likely pass the validation step since it is a common last name in the English language. However, it cannot be directly inserted into the database because it contains the "'" apostrophe character, which would need to be escaped or otherwise neutralized. In this case, stripping the apostrophe might reduce the risk of SQL injection, but it would produce incorrect behavior because the wrong name would be recorded.

Demonstrative Examples   (Details)

1. Consider a chat application in which a front-end web application communicates with a back-end server. The back-end is legacy code that does not perform authentication or authorization, so the front-end must implement it. The chat protocol supports two commands, SAY and BAN, although only administrators can use the BAN command. Each argument must be separated by a single space. The raw inputs are URL-encoded. The messaging protocol allows multiple commands to be specified on the same line if they are separated by a "|" character.
2. Here a value read from an HTML form parameter is reflected back to the client browser without having been encoded prior to output.
3. This example takes user input, passes it through an encoding scheme and then creates a directory specified by the user.

Observed Examples

1. CVE-2008-4636 : OS command injection in backup software using shell metacharacters in a filename; correct behavior would require that this filename could not be changed.
2. CVE-2008-0769 : Web application does not set the charset when sending a page to a browser, allowing for XSS exploitation when a browser chooses an unexpected encoding.
3. CVE-2008-0005 : Program does not set the charset when sending a page to a browser, allowing for XSS exploitation when a browser chooses an unexpected encoding.
4. CVE-2008-5573 : SQL injection via password parameter; a strong password might contain "&"
5. CVE-2008-3773 : Cross-site scripting in chat application via a message subject, which normally might contain "&" and other XSS-related characters.
6. CVE-2008-0757 : Cross-site scripting in chat application via a message, which normally might be allowed to contain arbitrary content.

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

References:

1. OWASP .OWASP Enterprise Security API (ESAPI) Project.
2. Jeremiah Grossman .Input validation or output filtering, which is better?.
3. Joshbw .Output Sanitization. 2008-09-18.
4. Niyaz PK .Sanitizing user data: How and where to do it. 2008-09-11.
5. Jeremiah Grossman .Input validation or output filtering, which is better?. 2007-01-30.
6. Jim Manico .Input Validation - Not That Important. 2008-08-10.
7. Michael Eddington .Preventing XSS with Correct Output Encoding.
8. M. Howard D. LeBlanc .Writing Secure Code 2nd Edition. Microsoft. Section:'Chapter 11, "Canonical Representation Issues" Page 363'. Published on 2002.