Incorporate diagnostic tests into your program using, for example, the assert() macro.

The assert macro expands to a void expression:

#include <assert.h>
void assert(scalar expression);

When it is executed, if expression (which must have a scalar type) is false, the assert macro outputs information about the failed assertion (including the text of the argument, the name of the source file, the source line number, and the name of the enclosing function) on the standard error stream, in an implementation-defined format, and calls the abort() function.

In the following example, the test for integer wrap was omitted for the unsigned multiplication on the assumption that MAX_TABLE_SIZE * sizeof(char *) cannot exceed SIZE_MAX. Although we know this is true, it cannot do any harm to codify this assumption.

assert(size <= SIZE_MAX/sizeof(char *));
table_size = size * sizeof(char *);

Assertions are primarily intended for use during debugging and are generally turned off before code is deployed by defining the NDEBUG macro (typically as a flag passed to the compiler). Consequently, assertions should be used to protect against incorrect programmer assumptions and not for runtime error checking.

Assertions should never be used to verify the absence of runtime (as opposed to logic) errors, such as

Code that protects against a buffer overflow, for example, cannot be implemented as an assertion because this code must be presented in the deployed executable.

In particular, assertions are generally unsuitable for server programs or embedded systems in deployment. A failed assertion can lead to a denial-of-service attack if triggered by a malicious user, such as size being derived, in some way, from client input. In such situations, a soft failure mode, such as writing to a log file and rejecting the request, is more appropriate.

if (size > SIZE_MAX / sizeof(char *)) {
  fprintf(log_file, "%s: size %zu exceeds %zu bytes\n",
          __FILE__, size, SIZE_MAX / sizeof(char *));
  size = SIZE_MAX / sizeof(char *);
table_size = size * sizeof(char *);

Noncompliant Code Example (malloc())

This noncompliant code example uses the assert() macro to verify that memory allocation succeeded. Because memory availability depends on the overall state of the system and can become exhausted at any point during a process lifetime, a robust program must be prepared to gracefully handle and recover from its exhaustion. Consequently, using the assert() macro to verify that a memory allocation succeeded would be inappropriate because doing so might lead to an abrupt termination of the process, opening the possibility of a denial-of-service attack. See also MEM11-C. Do not assume infinite heap space and void MEM32-C. Detect and handle memory allocation errors.

char *dupstring(const char *c_str) {
  size_t len;
  char *dup;

  len = strlen(c_str);
  dup = (char *)malloc(len + 1);
  assert(NULL != dup);

  memcpy(dup, c_str, len + 1);
  return dup;

Compliant Solution (malloc())

This compliant solution demonstrates how to detect and handle possible memory exhaustion:

char *dupstring(const char *c_str) {
  size_t len;
  char *dup;

  len = strlen(c_str);
  dup = (char*)malloc(len + 1);
  /* Detect and handle memory allocation error */
  if (NULL == dup) {
      return NULL; 

  memcpy(dup, c_str, len + 1);
  return dup;

Risk Assessment

Assertions are a valuable diagnostic tool for finding and eliminating software defects that may result in vulnerabilities. The absence of assertions, however, does not mean that code is incorrect.




Remediation Cost









Automated Detection





LANG.FUNCS.ASSERTSNot enough assertions



Can detect the specific instance where assertion contains an operation/function call that may have a side effect

Parasoft C/C++test
Assert liberally to document internal assumptions and invariants

Related Vulnerabilities

Search forĀ vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

CERT C Secure Coding StandardERR00-C. Adopt and implement a consistent and comprehensive error-handling policy
SEI CERT C++ Coding StandardVOID MSC11-CPP. Incorporate diagnostic tests using assertions
MITRE CWECWE-190, Reachable assertion