CWE-96: Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')
Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')
Weakness ID: 96 (Weakness Base)
The software 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.
Time of Introduction
Architecture and Design
All Interpreted Languages
Technical Impact: Read files or
directories; Read application
The injected code could access restricted data / files.
Technical Impact: Bypass protection
In some cases, injectable code controls authentication; this may lead
to a remote vulnerability.
Technical Impact: Gain privileges / assume
Injected code can access resources that the attacker is directly
prevented from accessing.
Technical Impact: Execute unauthorized code or
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.
Technical Impact: Hide activities
Often the actions performed by injected control code are
Enabling Factors for Exploitation
This issue is most 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.
This example attempts to write user messages to a message file and
allow users to view them.
chain: execution after redirect allows
non-administrator to perform static code
Strategy: Input Validation
Assume all input is malicious. Use an "accept known good" input
validation strategy, i.e., use a whitelist of acceptable inputs that
strictly conform to specifications. Reject any input that does not
strictly conform to specifications, or transform it into something that
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
(i.e., do not rely on a blacklist). A blacklist 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, blacklists can be useful for detecting potential
attacks or determining which inputs are so malformed that they should be
Strategy: Output Encoding
Perform proper output validation and escaping to neutralize all code
syntax from data written to code files.
the weakness exists independent of other weaknesses)
"HTML injection" (see CWE-79: XSS) could be thought of as an example of this, but the code is injected and executed on the client side, not the server side. Server-Side Includes (SSI) are an example of direct static code injection.