Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-96 Base Draft
Improper Neutralization of Directives in Statically Saved Code ('Static Code Injection')
Static Code Injection occurs when an application incorporates unvalidated or improperly sanitized user input directly into a static, executable resource like a configuration file, template, or…
Definition
What is CWE-96?
Static Code Injection occurs when an application incorporates unvalidated or improperly sanitized user input directly into a static, executable resource like a configuration file, template, or library. Because this input is saved and later executed, it allows an attacker to inject malicious code that becomes a permanent part of the application's logic.
This vulnerability is dangerous because the injected code becomes embedded within a file that the system trusts and executes automatically. Unlike attacks that only affect a single transaction, a successful static code injection can persistently compromise the application, leading to ongoing data theft, system takeover, or service disruption every time the compromised resource is used.
To prevent it, developers must treat all data destined for static files as untrusted. Implement strict input validation using allowlists for expected values and context-specific output encoding or sanitization before writing data to configuration files, templates, or scripts. Never construct executable code by simply concatenating user input.
Real-world impact
Real-world CVEs caused by CWE-96
-
Perl code directly injected into CGI library file from parameters to another CGI program.
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Direct PHP code injection into supporting template file.
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Direct code injection into PHP script that can be accessed by attacker.
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PHP code from User-Agent HTTP header directly inserted into log file implemented as PHP script.
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chain: execution after redirect allows non-administrator to perform static code injection.
How attackers exploit it
Step-by-step attacker path
- 1
This example attempts to write user messages to a message file and allow users to view them.
- 2
While the programmer intends for the MessageFile to only include data, an attacker can provide a message such as:
- 3
which will decode to the following:
- 4
The programmer thought they were just including the contents of a regular data file, but PHP parsed it and executed the code. Now, this code is executed any time people view messages.
- 5
Notice that XSS (CWE-79) is also possible in this situation.
Vulnerable code example
Vulnerable PHP
This example attempts to write user messages to a message file and allow users to view them.
$MessageFile = "messages.out";
if ($_GET["action"] == "NewMessage") {
$name = $_GET["name"];
$message = $_GET["message"];
$handle = fopen($MessageFile, "a+");
fwrite($handle, "<b>$name</b> says '$message'<hr>\n");
fclose($handle);
echo "Message Saved!<p>\n";
}
else if ($_GET["action"] == "ViewMessages") {
include($MessageFile);
} Attacker payload
While the programmer intends for the MessageFile to only include data, an attacker can provide a message such as:
name=h4x0r
message=%3C?php%20system(%22/bin/ls%20-l%22);?%3E Secure code example
Secure pseudo
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
const safe = validateAndEscape(input);
return executeWithGuards(safe);
} What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist
How to prevent CWE-96
- Implementation 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 Perform proper output validation and escaping to neutralize all code syntax from data written to code files.
Detection signals
How to detect CWE-96
Run dynamic application security testing against the live endpoint.
Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.
Code review: flag any new code that handles input from this surface without using the validated framework helpers.
Plexicus auto-detects CWE-96 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-96?
How serious is CWE-96?
What languages or platforms are affected by CWE-96?
How can I prevent CWE-96?
How does Plexicus detect and fix CWE-96?
Where can I learn more about CWE-96?
Frequently asked questions
What is CWE-96?
Static Code Injection occurs when an application incorporates unvalidated or improperly sanitized user input directly into a static, executable resource like a configuration file, template, or library. Because this input is saved and later executed, it allows an attacker to inject malicious code that becomes a permanent part of the application's logic.
How serious is CWE-96?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-96?
MITRE lists the following affected platforms: PHP, Perl, Interpreted.
How can I prevent CWE-96?
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…
How does Plexicus detect and fix CWE-96?
Plexicus's SAST engine matches the data-flow signature for CWE-96 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-96?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/96.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-96
CWE-94 Parent
Improper Control of Generation of Code ('Code Injection')
This vulnerability occurs when an application builds executable code using unvalidated external input, such as user data. Because the…
CWE-1336 Sibling
Improper Neutralization of Special Elements Used in a Template Engine
This vulnerability occurs when an application uses a template engine to process user-controlled input but fails to properly sanitize…
CWE-95 Sibling
Improper Neutralization of Directives in Dynamically Evaluated Code ('Eval Injection')
This vulnerability occurs when an application takes user input and passes it directly into a dynamic code execution function, like eval(),…
CWE-97 Child
Improper Neutralization of Server-Side Includes (SSI) Within a Web Page
This vulnerability occurs when a web application dynamically generates pages but fails to properly sanitize user-supplied input that could…
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