CWE-252: Unchecked Return Value

Description:
The product does not check the return value from a method or function, which can prevent it from detecting unexpected states and conditions.

Extended Description:
Two common programmer assumptions are "this function call can never fail" and "it doesn't matter if this function call fails". If an attacker can force the function to fail or otherwise return a value that is not expected, then the subsequent program logic could lead to a vulnerability, because the product is not in a state that the programmer assumes. For example, if the program calls a function to drop privileges but does not check the return code to ensure that privileges were successfully dropped, then the program will continue to operate with the higher privileges.

Affected languages: Not Language-Specific
Parent weaknesses: CWE-754, CWE-754

Consequences:
  - Availability: Unexpected State

Detection methods:
  - 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 havin

Mitigations:
  - [Implementation] Check the results of all functions that return a value and verify that the value is expected.
  - [Implementation] For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has f
  - [Implementation] Ensure that you account for all possible return values from the function.
  - [Implementation] When designing a function, make sure you return a value or throw an exception in case of an error.

Demonstrative examples:
Consider the following code segment:
The programmer expects that when fgets() returns, buf will contain a null-terminated string of length 9 or less. But if an I/O error occurs, fgets() will not null-terminate buf. Furthermore, if the end of the file is reached before any characters are read, fgets() returns without writing anything to buf. In both of these situations, fgets() signals that something unusual has happened by returning NULL, but in this code, the warning will not be noticed. The lack of a null terminator in buf can result in a buffer overflow in the subsequent call to strcpy().
char buf[10], cp_buf[10]; fgets(buf, 10, stdin); strcpy(cp_buf, buf);

In the following example, it is possible to request that memcpy move a much larger segment of memory than assumed:
If returnChunkSize() happens to encounter an error it will return -1. Notice that the return value is not checked before the memcpy operation (CWE-252), so -1 can be passed as the size argument to memcpy() (CWE-805). Because memcpy() assumes that the value is unsigned, it will be interpreted as MAXINT-1 (CWE-195), and therefore will copy far more memory than is likely available to the destination buffer (CWE-787, CWE-788).
int returnChunkSize(void *) { 
                         
                            
                            /* if chunk info is valid, return the size of usable memory, 
                            
                            
                        

Real-world examples:
  - CVE-2020-17533: Chain: unchecked return value (CWE-252) of some functions for policy enforcement leads to authorization bypass (CWE-862)
  - CVE-2020-6078: Chain: The return value of a function returning a pointer is not checked for success (CWE-252) resulting in the later use of an uninitialized variable (CWE-456) and a null pointer dereference (CWE-476
  - CVE-2019-15900: Chain: sscanf() call is used to check if a username and group exists, but the return value of sscanf() call is not checked (CWE-252), causing an uninitialized variable to be checked (CWE-457), returni
  - CVE-2007-3798: Unchecked return value leads to resultant integer overflow and code execution.
  - CVE-2006-4447: Program does not check return value when invoking functions to drop privileges, which could leave users with higher privileges than expected by forcing those functions to fail.