Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-253 Base Incomplete
Incorrect Check of Function Return Value
This vulnerability occurs when a program misinterprets or improperly validates the return value from a function, causing it to miss critical error states or unexpected conditions.
Definition
What is CWE-253?
This vulnerability occurs when a program misinterprets or improperly validates the return value from a function, causing it to miss critical error states or unexpected conditions.
Many critical functions, especially those dealing with system resources, memory, files, or network connections, communicate success or failure through their return values. A developer must correctly check these values to understand if the operation completed as expected or if an error occurred that requires handling, such as a failed memory allocation or a closed network socket.
Failing to perform accurate checks often leads to the program continuing execution as if nothing is wrong, even when it's operating on invalid data, null pointers, or corrupted states. This creates a gap between the actual error and the program's awareness of it, allowing subsequent operations to fail silently or behave unpredictably, which can lead to crashes, data corruption, or security bypasses.
Real-world impact
Real-world CVEs caused by CWE-253
-
Chain: function in web caching proxy does not correctly check a return value (CWE-253) leading to a reachable assertion (CWE-617)
How attackers exploit it
Step-by-step attacker path
- 1
Identify a code path that handles untrusted input without validation.
- 2
Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.
- 3
Deliver the payload through a normal request and observe the application's reaction.
- 4
Iterate until the response leaks data, executes attacker code, or escalates privileges.
Vulnerable code example
Vulnerable C
This code attempts to allocate memory for 4 integers and checks if the allocation succeeds.
tmp = malloc(sizeof(int) * 4);
if (tmp < 0 ) {
perror("Failure");
```
//should have checked if the call returned 0*
} 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-253
- Architecture and Design Use a language or compiler that uses exceptions and requires the catching of those exceptions.
- Implementation Properly check all functions which return a value.
- Implementation When designing any function make sure you return a value or throw an exception in case of an error.
Detection signals
How to detect CWE-253
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-253 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-253?
How serious is CWE-253?
What languages or platforms are affected by CWE-253?
How can I prevent CWE-253?
How does Plexicus detect and fix CWE-253?
Where can I learn more about CWE-253?
Frequently asked questions
What is CWE-253?
This vulnerability occurs when a program misinterprets or improperly validates the return value from a function, causing it to miss critical error states or unexpected conditions.
How serious is CWE-253?
MITRE rates the likelihood of exploit as Low — exploitation is uncommon, but the weakness should still be fixed when discovered.
What languages or platforms are affected by CWE-253?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent CWE-253?
Use a language or compiler that uses exceptions and requires the catching of those exceptions. Properly check all functions which return a value.
How does Plexicus detect and fix CWE-253?
Plexicus's SAST engine matches the data-flow signature for CWE-253 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-253?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/253.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-253
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