CAPEC-135: Format String Injection

Description

An adversary includes formatting characters in a string input field on the target application. Most applications assume that users will provide static text and may respond unpredictably to the presence of formatting character. For example, in certain functions of the C programming languages such as printf, the formatting character %s will print the contents of a memory location expecting this location to identify a string and the formatting character %n prints the number of DWORD written in the memory. An adversary can use this to read or write to memory locations or files, or simply to manipulate the value of the resulting text in unexpected ways. Reading or writing memory may result in program crashes and writing memory could result in the execution of arbitrary code if the adversary can write to the program stack.

Extended Description

Many applications allow users to send email messages by filling in fields. For example, a web site may have a link to "share this site with a friend" where the user provides the recipient's email address and the web application fills out all the other fields, such as the subject and body. In this pattern, an adversary adds header and body information to an email message by injecting additional content in an input field used to construct a header of the mail message. This attack takes advantage of the fact that RFC 822 requires that headers in a mail message be separated by a carriage return. As a result, an adversary can inject new headers or content simply by adding a delimiting carriage return and then supplying the new heading and body information. This attack will not work if the user can only supply the message body since a carriage return in the body is treated as a normal character.

Severity :

High

Possibility :

High

Type :

Standard

Relationships with other CAPECs

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

CAPEC-67: String Format Overflow in syslog() String Format Overflow in syslog() CAPEC-137: Parameter Injection Parameter Injection

Prerequisites

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

The target application must accept a strings as user input, fail to sanitize string formatting characters in the user input, and process this string using functions that interpret string formatting characters.

Skills required

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

High In order to discover format string vulnerabilities it takes only low skill, however, converting this discovery into a working exploit requires advanced knowledge on the part of the adversary.

Taxonomy mappings

Mappings to ATT&CK, OWASP and other frameworks.

OWASP Attacks | Format string attack

Resources required

None: No specialized resources are required to execute this type of attack.

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.

CWE-20: Improper Input Validation

CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

CWE-134: Use of Externally-Controlled Format String

Visit http://capec.mitre.org/ for more details.