COMMON WEAKNESS ENUMERATIONDraft

CWE-96

Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')

The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes code syntax before inserting the input into an executable resource, such as a library, configuration file, or template.

Abstraction

Base

Structure

Simple

Likelihood of Exploit

Medium

Understand the problem

What is the problem?

The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes code syntax before inserting the input into an executable resource, such as a library, configuration file, or template.

Root cause

How and when does the problem arise?

Lifecycle phase

Implementation

REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Lifecycle phase

Implementation

This issue is frequently found in PHP applications that allow users to set configuration variables that are stored within executable PHP files. Technically, this could also be performed in some compiled code (e.g., by byte-patching an executable), although it is highly unlikely.

Risk

What does successful exploitation lead to?

Read Files or DirectoriesRead Application Data

Affected security scopes: Confidentiality

The injected code could access restricted data / files.
Bypass Protection Mechanism

Affected security scopes: Access Control

In some cases, injectable code controls authentication; this may lead to a remote vulnerability.
Gain Privileges or Assume Identity

Affected security scopes: Access Control

Injected code can access resources that the attacker is directly prevented from accessing.
Execute Unauthorized Code or Commands

Affected security scopes: Integrity, Confidentiality, Availability, Other

Code injection attacks can lead to loss of data integrity in nearly all cases as the control-plane data injected is always incidental to data recall or writing. Additionally, code injection can often result in the execution of arbitrary code.
Hide Activities

Affected security scopes: Non-Repudiation

Often the actions performed by injected control code are unlogged.

Defence

How is it prevented and fixed?

Implementation

Input Validation

Detail
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Implementation

Output Encoding

Detail
Perform proper output validation and escaping to neutralize all code syntax from data written to code files.

Verification

How is it detected?

Automated Static Analysis

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)