CWE-690 Compound Draft

Unchecked Return Value to NULL Pointer Dereference

This vulnerability occurs when a program calls a function that can return a NULL pointer to signal failure, but the code does not check for this error condition before using the returned value,…

Definition

What is CWE-690?

This vulnerability occurs when a program calls a function that can return a NULL pointer to signal failure, but the code does not check for this error condition before using the returned value, leading to a crash or unexpected behavior from dereferencing the NULL pointer.

Many functions in C and similar languages use a NULL pointer return value to indicate that an operation failed, such as when memory allocation fails or a required resource isn't found. If a developer assumes the call was always successful and uses the return value directly—for example, by trying to read or write to that memory location—the program will attempt to dereference NULL, typically causing a segmentation fault and a crash. This is a specific and common case of a broader class of unchecked return value errors. While not all functions signal errors with NULL (some use special integers or status codes), the pattern of failing to validate a function's output before proceeding is a frequent source of instability. Properly handling these potential NULL returns by adding checks is a fundamental practice for writing robust and secure software that can gracefully manage unexpected states.

Real-world impact

Real-world CVEs caused by CWE-690

CVE-2008-1052

Large Content-Length value leads to NULL pointer dereference when malloc fails.
CVE-2006-6227

Large message length field leads to NULL pointer dereference when malloc fails.
CVE-2006-2555

Parsing routine encounters NULL dereference when input is missing a colon separator.
CVE-2003-1054

URI parsing API sets argument to NULL when a parsing failure occurs, such as when the Referer header is missing a hostname, leading to NULL dereference.
CVE-2008-5183

chain: unchecked return value can lead to NULL dereference

How attackers exploit it

Step-by-step attacker path

1
The code below makes a call to the getUserName() function but doesn't check the return value before dereferencing (which may cause a NullPointerException).
2
This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer.
3
If an attacker provides an address that appears to be well-formed, but the address does not resolve to a hostname, then the call to gethostbyaddr() will return NULL. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference (CWE-476) would then occur in the call to strcpy().
4
Note that this code is also vulnerable to a buffer overflow (CWE-119).

Vulnerable code example

Vulnerable Java

The code below makes a call to the getUserName() function but doesn't check the return value before dereferencing (which may cause a NullPointerException).

Vulnerable Java

String username = getUserName();
  if (username.equals(ADMIN_USER)) {
  	...
  }

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-690

Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
Implementation Validate input at trust boundaries; use allowlists, not denylists.
Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
Operation Monitor logs for the runtime signals listed in the next section.

Detection signals

How to detect CWE-690

Black Box

This typically occurs in rarely-triggered error conditions, reducing the chances of detection during black box testing.

White Box

Code analysis can require knowledge of API behaviors for library functions that might return NULL, reducing the chances of detection when unknown libraries are used.

Plexicus auto-fix

Plexicus auto-detects CWE-690 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.

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Frequently asked questions

What is CWE-690?

How serious is CWE-690?

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-690?

MITRE lists the following affected platforms: C, C++.

How can I prevent CWE-690?

Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.

How does Plexicus detect and fix CWE-690?

Plexicus's SAST engine matches the data-flow signature for CWE-690 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-690?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/690.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-690

CWE-252 Parent