ByteOS Network

CAPEC-52:Embedding NULL Bytes

Attack Pattern ID:52

Version:v3.9

Attack Pattern Name:Embedding NULL Bytes

Abstraction:Detailed

Status:Draft

Likelihood of Attack:High

Typical Severity:High

Details Content History Related Weaknesses Reports

▼Description

An adversary embeds one or more null bytes in input to the target software. This attack relies on the usage of a null-valued byte as a string terminator in many environments. The goal is for certain components of the target software to stop processing the input when it encounters the null byte(s).

▼Relationships

Nature	Type	ID	Name
ChildOf	S	267	Leverage Alternate Encoding

Nature: ChildOf

Type: Standard

ID: 267

Name: Leverage Alternate Encoding

▼Execution Flow

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.

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) 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

Exploit

Remove data after null byte(s)

After determined entry points that are vulnerable, the adversary places a null byte(s) such that they 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) at the end of the input to try to traverse to the given directory.

▼Prerequisites

The program does not properly handle postfix NULL terminators

▼Skills Required

Medium

Directory traversal

High

Execution of arbitrary code

▼Consequences

Scope	Likelihood	Impact	Note
Integrity	N/A	Modify Data	N/A
Confidentiality	N/A	Read Data	N/A
ConfidentialityAccess ControlAuthorization	N/A	Gain Privileges	N/A
ConfidentialityIntegrityAvailability	N/A	Execute Unauthorized Commands	Run Arbitrary Code

Scope: Integrity

Likelihood: N/A

Impact: Modify Data

Note: N/A

Scope: Confidentiality

Likelihood: N/A

Impact: Read Data

Note: N/A

Scope: Confidentiality, Access Control, Authorization

Likelihood: N/A

Impact: Gain Privileges

Note: N/A

Scope: Confidentiality, Integrity, Availability

Likelihood: N/A

Impact: Execute Unauthorized Commands

Note: Run Arbitrary Code

▼Mitigations

Properly handle the NULL characters supplied as part of user input prior to doing anything with the data.

▼Example Instances

▼Related Weaknesses

ID	Name
CWE-158	Improper Neutralization of Null Byte or NUL Character
CWE-172	Encoding Error
CWE-173	Improper Handling of Alternate Encoding
CWE-20	Improper Input Validation
CWE-697	Incorrect Comparison
CWE-707	Improper Neutralization
CWE-74	Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')