|
|
| Home > CAPEC List > Individual CAPEC Dictionary Definition (Release 1.1) | View the CAPEC List |
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Individual CAPEC Dictionary Definition (Release 1.1)
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Using Escaped Slashes in Alternate Encoding | |||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Attack Pattern ID | Pattern Abstraction: Detailed 78 | ||||||||||||||||||||||||||||||||||||
| Typical Severity | High | ||||||||||||||||||||||||||||||||||||
| Description | Summary This attack targets the use of the backslash in alternate encoding. An attacker can provide a backslash as a leading character and causes a parser to believe that the next character is special. This is called an escape. By using that trick, the attacker tries to exploit alternate ways to encode the same character which leads to filter problems and opens avenues to attack. Attack Execution Flow
| ||||||||||||||||||||||||||||||||||||
| Attack Prerequisites | The application accepts the backlash character as escape character. The application server does incomplete input data decoding, filtering and validation. | ||||||||||||||||||||||||||||||||||||
| Typical Likelihood of Exploit | High | ||||||||||||||||||||||||||||||||||||
| Methods of Attack |
| ||||||||||||||||||||||||||||||||||||
| Examples-Instances | Description For example, the byte pair \0 might result in a single zero byte (a NULL) being sent. Another example is \t, which is sometimes converted into a tab character. There is often an equivalent encoding between the back slash and the escaped back slash. This means that \/ results in a single forward slash. A single forward slash also results in a single forward slash. The encoding looks like this: Description Attack Example: Escaped Slashes in Alternate Encodings | ||||||||||||||||||||||||||||||||||||
| Attacker Skill or Knowledge Required | Low - The attacker can naively try backslash character and discover that the target host uses it as escape character. Medium - The attacker may need deep understanding of the host target in order to exploit the vulnerability. The attacker may also use automated tools to probe for this vulnerability. | ||||||||||||||||||||||||||||||||||||
| Probing Techniques | An attacker can manually inject backslash characters in the data sent to the target host and observe the results of the request. The attacker may also run scripts or automated tools against the target host to uncover a vulnerability related to the use of the backslash character. | ||||||||||||||||||||||||||||||||||||
| Indicators-Warnings of Attack | A attacker can use a fuzzer in order to probe for this vulnerability. The fuzzer should generate suspicious network activity noticeable by an intrusion detection system. | ||||||||||||||||||||||||||||||||||||
| Obfuscation Techniques | Alternative method of data encoding can be used. | ||||||||||||||||||||||||||||||||||||
| Solutions and Mitigations | Verify that the user-supplied data does not use backslash character to escape malicious characters. Assume all input is malicious. Create a white list that defines all valid input to the software system based on the requirements specifications. Input that does not match against the white list should not be permitted to enter into the system. Be aware of the threat of alternative method of data encoding. Regular expressions can be used to filter out backslash. Make sure you decode before filtering and validating the untrusted input data. In the case of path traversals, use the principle of least privilege when determining access rights to file systems. Do not allow users to access directories/files that they should not access. Any security checks should occur after the data has been decoded and validated as correct data format. Do not repeat decoding process, if bad character are left after decoding process, treat the data as suspicious, and fail the validation process. Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names. | ||||||||||||||||||||||||||||||||||||
| Attack Motivation- |
| ||||||||||||||||||||||||||||||||||||
| Injection Vector | The user supplied data (e.g., HTTP request) | ||||||||||||||||||||||||||||||||||||
| Payload | The backslash character injected in the user supplied data. The backslash character can be obfuscated with alternate encoding. | ||||||||||||||||||||||||||||||||||||
| Activation Zone | The command or request interpreter used on the host target may consider the backslash character as escape character. | ||||||||||||||||||||||||||||||||||||
| Payload Activation Impact | The character following the backslash character will be escaped (i.e, unfiltered) and may cause harmful effects. | ||||||||||||||||||||||||||||||||||||
| Related Weaknesses |
| ||||||||||||||||||||||||||||||||||||
| Related Attack Patterns |
| ||||||||||||||||||||||||||||||||||||
| Relevant Security Requirements | All client-supplied input must be validated through filtering and all output must be properly escaped. | ||||||||||||||||||||||||||||||||||||
| Related Security Principles |
| ||||||||||||||||||||||||||||||||||||
| Related Guidelines |
| ||||||||||||||||||||||||||||||||||||
| Purpose | Penetration Exploitation | ||||||||||||||||||||||||||||||||||||
| CIA Impact |
| ||||||||||||||||||||||||||||||||||||
| Technical Context |
| ||||||||||||||||||||||||||||||||||||
| References | G. Hoglund and G. McGraw. Exploiting Software: How to Break Code. Addison-Wesley, February 2004. CWE – Input Validation | ||||||||||||||||||||||||||||||||||||
| Source |
| ||||||||||||||||||||||||||||||||||||
|
|
|