1799
If the application is unable to extract the state information - say, due to a database timeout - then
the $uid variable will not be explicitly set by the programmer. This will cause $uid to be regarded as
equivalent to "0" in the conditional, allowing the original user to perform administrator actions. Even
if the attacker cannot directly influence the state data, unexpected errors could cause incorrect
privileges to be assigned to a user just by accident.
Example 3:
The following code intends to concatenate a string to a variable and print the string.
Example Language: C (Bad)
char str[20];
strcat(str, "hello world");
printf("%s", str);
This might seem innocent enough, but str was not initialized, so it contains random memory. As a
result, str[0] might not contain the null terminator, so the copy might start at an offset other than 0.
The consequences can vary, depending on the underlying memory.
If a null terminator is found before str[8], then some bytes of random garbage will be printed before
the "hello world" string. The memory might contain sensitive information from previous uses, such
as a password (which might occur as a result of CWE-14 or CWE-244). In this example, it might not
be a big deal, but consider what could happen if large amounts of memory are printed out before
the null terminator is found.
If a null terminator isn't found before str[8], then a buffer overflow could occur, since strcat will first
look for the null terminator, then copy 12 bytes starting with that location. Alternately, a buffer overread
might occur (CWE-126) if a null terminator isn't found before the end of the memory segment
is reached, leading to a segmentation fault and crash.
Example 4:
This example will leave test_string in an unknown condition when i is the same value as err_val,
because test_string is not initialized (CWE-456). Depending on where this code segment appears
(e.g. within a function body), test_string might be random if it is stored on the heap or stack. If
the variable is declared in static memory, it might be zero or NULL. Compiler optimization might
contribute to the unpredictability of this address.
Example Language: C (Bad)
char *test_string;
if (i != err_val)
{
test_string = "Hello World!";
}
printf("%s", test_string);
When the printf() is reached, test_string might be an unexpected address, so the printf might print
junk strings (CWE-457).
To fix this code, there are a couple approaches to making sure that test_string has been properly
set once it reaches the printf().
One solution would be to set test_string to an acceptable default before the conditional:
Example Language: C (Good)
char *test_string = "Done at the beginning";
if (i != err_val)
{
test_string = "Hello World!";
}
CWE Version 4.14
CWE-910: Use of Expired File Descriptor
CWE-910: Use of Expired File Descriptor