CAPEC-53
Postfix, Null Terminate, and Backslash
HIGH
HIGH
Draft
2014-06-23 00:00 +00:00
2022-09-29 00:00 +00:00
Alerte pour un CAPEC
Restez informé de toutes modifications pour un CAPEC spécifique.
Description
If a string is passed through a filter of some kind, then a terminal NULL may not be valid. Using alternate representation of NULL allows an adversary to embed the NULL mid-string while postfixing the proper data so that the filter is avoided. One example is a filter that looks for a trailing slash character. If a string insertion is possible, but the slash must exist, an alternate encoding of NULL in mid-string may be used.
Informations
Execution Flow
1) Explore
[Survey the application for user-controllable inputs] Using a browser, an automated tool or by inspecting the application, an adversary records all entry points to the application.
Technique
- Use a spidering tool to follow and record all links and analyze the web pages to find entry points. Make special note of any links that include parameters in the URL.
- Use a proxy tool to record all user input entry points visited during a manual traversal of the web application.
- Use a browser to manually explore the website and analyze how it is constructed. Many browsers' plugins are available to facilitate the analysis or automate the discovery.
- Manually inspect the application to find entry points.
2) Experiment
[Probe entry points to locate vulnerabilities] The adversary uses the entry points gathered in the "Explore" phase as a target list and injects postfix null byte(s) followed by a backslash to observe how the application handles them as input. The adversary is looking for areas where user input is placed in the middle of a string, and the null byte causes the application to stop processing the string at the end of the user input.
Technique
- Try different encodings for null such as \0 or %00 followed by an encoding for the backslash character.
3) Exploit
[Remove data after null byte(s)] After determined entry points that are vulnerable, the adversary places a null byte(s) followed by a backslash such that they bypass an input filter and remove data after the null byte(s) in a way that is beneficial to them.
Technique
- If the input is a directory as part of a longer file path, add a null byte(s) followed by a backslash at the end of the input to try to traverse to the given directory.
Prerequisites
Null terminators are not properly handled by the filter.Skills Required
An adversary needs to understand alternate encodings, what the filter looks for and the data format acceptable to the target APIMitigations
Properly handle Null characters. Make sure canonicalization is properly applied. Do not pass Null characters to the underlying APIs.Assume all input is malicious. Create an allowlist that defines all valid input to the software system based on the requirements specifications. Input that does not match against the allowlist should not be permitted to enter into the system.
Faiblesses connexes
| Nom de la faiblesse | |
|---|---|
| Improper Neutralization of Null Byte or NUL Character The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes NUL characters or null bytes when they are sent to a downstream component. |
|
| Encoding Error The product does not properly encode or decode the data, resulting in unexpected values. |
|
| Improper Handling of Alternate Encoding The product does not properly handle when an input uses an alternate encoding that is valid for the control sphere to which the input is being sent. |
|
| Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component. |
|
| Improper Input Validation The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. |
|
| Incorrect Comparison The product compares two entities in a security-relevant context, but the comparison is incorrect, which may lead to resultant weaknesses. |
|
| Improper Neutralization The product does not ensure or incorrectly ensures that structured messages or data are well-formed and that certain security properties are met before being read from an upstream component or sent to a downstream component. |
References
REF-1
Exploiting Software: How to Break CodeG. Hoglund, G. McGraw.
Submission
| Name | Organization | Date | Date Release |
|---|---|---|---|
| CAPEC Content Team | The MITRE Corporation |
Modifications
| Name | Organization | Date | Comment |
|---|---|---|---|
| CAPEC Content Team | The MITRE Corporation | Updated Related_Attack_Patterns | |
| CAPEC Content Team | The MITRE Corporation | Updated Mitigations | |
| CAPEC Content Team | The MITRE Corporation | Updated Related_Weaknesses | |
| CAPEC Content Team | The MITRE Corporation | Updated Description, Execution_Flow, Skills_Required | |
| CAPEC Content Team | The MITRE Corporation | Updated Example_Instances |
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