CWE-805: Buffer Access with Incorrect Length Value
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Edit Custom FilterThe product uses a sequential operation to read or write a buffer, but it uses an incorrect length value that causes it to access memory that is outside of the bounds of the buffer.
When the length value exceeds the size of the destination, a buffer overflow could occur.
This table specifies different individual consequences
associated with the weakness. The Scope identifies the application security area that is
violated, while the Impact describes the negative technical impact that arises if an
adversary succeeds in exploiting this weakness. The Likelihood provides information about
how likely the specific consequence is expected to be seen relative to the other
consequences in the list. For example, there may be high likelihood that a weakness will be
exploited to achieve a certain impact, but a low likelihood that it will be exploited to
achieve a different impact.
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Relevant to the view "Research Concepts" (CWE-1000)
Relevant to the view "Software Development" (CWE-699)
Relevant to the view "CISQ Quality Measures (2020)" (CWE-1305)
Relevant to the view "CISQ Data Protection Measures" (CWE-1340)
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weakness appears for that instance.
Languages C (Often Prevalent) C++ (Often Prevalent) Class: Assembly (Undetermined Prevalence) Example 1 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. (bad code)
Example Language: C
void host_lookup(char *user_supplied_addr){
struct hostent *hp;
in_addr_t *addr; char hostname[64]; in_addr_t inet_addr(const char *cp); /*routine that ensures user_supplied_addr is in the right format for conversion */ validate_addr_form(user_supplied_addr); addr = inet_addr(user_supplied_addr); hp = gethostbyaddr( addr, sizeof(struct in_addr), AF_INET); strcpy(hostname, hp->h_name); This function allocates a buffer of 64 bytes to store the hostname under the assumption that the maximum length value of hostname is 64 bytes, however there is no guarantee that the hostname will not be larger than 64 bytes. If an attacker specifies an address which resolves to a very large hostname, then the function may overwrite sensitive data or even relinquish control flow to the attacker. Note that this example also contains an unchecked return value (CWE-252) that can lead to a NULL pointer dereference (CWE-476). Example 2 In the following example, it is possible to request that memcpy move a much larger segment of memory than assumed: (bad code)
Example Language: C
int returnChunkSize(void *) {
/* if chunk info is valid, return the size of usable memory, * else, return -1 to indicate an error */ ... int main() { ... }memcpy(destBuf, srcBuf, (returnChunkSize(destBuf)-1)); ... 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). Example 3 In the following example, the source character string is copied to the dest character string using the method strncpy. (bad code)
Example Language: C
...
char source[21] = "the character string"; char dest[12]; strncpy(dest, source, sizeof(source)-1); ... However, in the call to strncpy the source character string is used within the sizeof call to determine the number of characters to copy. This will create a buffer overflow as the size of the source character string is greater than the dest character string. The dest character string should be used within the sizeof call to ensure that the correct number of characters are copied, as shown below. (good code)
Example Language: C
...
char source[21] = "the character string"; char dest[12]; strncpy(dest, source, sizeof(dest)-1); ... Example 4 In this example, the method outputFilenameToLog outputs a filename to a log file. The method arguments include a pointer to a character string containing the file name and an integer for the number of characters in the string. The filename is copied to a buffer where the buffer size is set to a maximum size for inputs to the log file. The method then calls another method to save the contents of the buffer to the log file. (bad code)
Example Language: C
#define LOG_INPUT_SIZE 40
// saves the file name to a log file int outputFilenameToLog(char *filename, int length) { int success;
// buffer with size set to maximum size for input to log file char buf[LOG_INPUT_SIZE]; // copy filename to buffer strncpy(buf, filename, length); // save to log file success = saveToLogFile(buf); return success; However, in this case the string copy method, strncpy, mistakenly uses the length method argument to determine the number of characters to copy rather than using the size of the local character string, buf. This can lead to a buffer overflow if the number of characters contained in character string pointed to by filename is larger then the number of characters allowed for the local character string. The string copy method should use the buf character string within a sizeof call to ensure that only characters up to the size of the buf array are copied to avoid a buffer overflow, as shown below. (good code)
Example Language: C
...
// copy filename to buffer strncpy(buf, filename, sizeof(buf)-1); ... Example 5 Windows provides the MultiByteToWideChar(), WideCharToMultiByte(), UnicodeToBytes(), and BytesToUnicode() functions to convert between arbitrary multibyte (usually ANSI) character strings and Unicode (wide character) strings. The size arguments to these functions are specified in different units, (one in bytes, the other in characters) making their use prone to error. In a multibyte character string, each character occupies a varying number of bytes, and therefore the size of such strings is most easily specified as a total number of bytes. In Unicode, however, characters are always a fixed size, and string lengths are typically given by the number of characters they contain. Mistakenly specifying the wrong units in a size argument can lead to a buffer overflow. The following function takes a username specified as a multibyte string and a pointer to a structure for user information and populates the structure with information about the specified user. Since Windows authentication uses Unicode for usernames, the username argument is first converted from a multibyte string to a Unicode string. (bad code)
Example Language: C
void getUserInfo(char *username, struct _USER_INFO_2 info){
WCHAR unicodeUser[UNLEN+1]; }MultiByteToWideChar(CP_ACP, 0, username, -1, unicodeUser, sizeof(unicodeUser)); NetUserGetInfo(NULL, unicodeUser, 2, (LPBYTE *)&info); This function incorrectly passes the size of unicodeUser in bytes instead of characters. The call to MultiByteToWideChar() can therefore write up to (UNLEN+1)*sizeof(WCHAR) wide characters, or (UNLEN+1)*sizeof(WCHAR)*sizeof(WCHAR) bytes, to the unicodeUser array, which has only (UNLEN+1)*sizeof(WCHAR) bytes allocated. If the username string contains more than UNLEN characters, the call to MultiByteToWideChar() will overflow the buffer unicodeUser.
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reference this weakness as a member. This information is often useful in understanding where a
weakness fits within the context of external information sources.
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