|ID: 193||Date: (C)2012-05-14 (M)2020-05-20|
|Type: weakness||Status: DRAFT|
|Abstraction Type: Base|
A product calculates or uses an incorrect maximum or minimum
value that is 1 more, or 1 less, than the correct value.
Applicable PlatformsLanguage Class: All
Time Of Introduction
|Availability ||DoS: crash / exit /
restartDoS: resource consumption
(CPU)DoS: resource consumption
(memory)DoS: instability ||This weakness will generally lead to undefined behavior and therefore
crashes. In the case of overflows involving loop index variables, the
likelihood of infinite loops is also high. |
|Integrity ||Modify memory ||If the value in question is important to data (as opposed to flow),
simple data corruption has occurred. Also, if the wrap around results in
other conditions such as buffer overflows, further memory corruption may
|ConfidentialityAvailabilityAccess_Control ||Execute unauthorized code or
mechanism ||This weakness can sometimes trigger buffer overflows which can be used
to execute arbitrary code. This is usually outside the scope of a
program's implicit security policy. |
|Implementation || ||When copying character arrays or using character manipulation
methods, the correct size parameter must be used to account for the null
terminator that needs to be added at the end of the array. Some examples
of functions susceptible to this weakness in C include strcpy(),
strncpy(), strcat(), strncat(), printf(), sprintf(), scanf() and
sscanf(). || || |
RelationshipsThis is not always a buffer overflow. For example, an off-by-one error
could be a factor in a partial comparison, a read from the wrong memory
location, an incorrect conditional, etc.
|CWE-193 ChildOf CWE-907 ||Category ||CWE-888 || |
Demonstrative Examples (Details)
- As another example the Off-by-one error can occur when using the
sprintf library function to copy a string variable to a formatted string
variable and the original string variable comes from an untrusted source. As
in the following example where a local function, setFilename is used to
store the value of a filename to a database but first uses sprintf to format
the filename. The setFilename function includes an input parameter with the
name of the file that is used as the copy source in the sprintf function.
The sprintf function will copy the file name to a char array of size 20 and
specifies the format of the new variable as 16 characters followed by the
file extension .dat.
- Similarly, this example uses the strncat and snprintf functions
incorrectly. The code does not account for the null character that is added
by the second strncat function call, one byte beyond the end of the name
- The Off-by-one error can also be manifested when reading characters
of a character array using a for loop that has the incorrect size as a
continuation condition and attempts to read beyond the end of the buffer for
the character array as shown in the following example.
- The following C/C++ example demonstrates the Off-by-one error in the
main method of a pattern matching utility that looks for a specific pattern
within a specific file. The main method uses the string copy method,
strncpy, to copy the command line user input file name and pattern to the
Filename and Pattern character arrays respectively.
- The following code allocates memory for a maximum number of widgets.
It then gets a user-specified number of widgets, making sure that the user
does not request too many. It then initializes the elements of the array
using InitializeWidget(). Because the number of widgets can vary for each
request, the code inserts a NULL pointer to signify the location of the last
widget. (Demonstrative Example Id DX-20)
- CVE-2003-0252 : Off-by-one error allows remote attackers to cause a denial of service and possibly execute arbitrary code via requests that do not contain newlines.
- CVE-2001-1391 : Off-by-one vulnerability in driver allows users to modify kernel memory.
- CVE-2002-0083 : Off-by-one error allows local users or remote malicious servers to gain privileges.
- CVE-2002-0653 : Off-by-one buffer overflow in function usd by server allows local users to execute arbitrary code as the server user via .htaccess files with long entries.
- CVE-2002-0844 : Off-by-one buffer overflow in version control system allows local users to execute arbitrary code.
- CVE-1999-1568 : Off-by-one error in FTP server allows a remote attacker to cause a denial of service (crash) via a long PORT command.
- CVE-2004-0346 : Off-by-one buffer overflow in FTP server allows local users to gain privileges via a 1024 byte RETR command.
- CVE-2004-0005 : Multiple buffer overflows in chat client allow remote attackers to cause a denial of service and possibly execute arbitrary code.
- CVE-2003-0356 : Multiple off-by-one vulnerabilities in product allow remote attackers to cause a denial of service and possibly execute arbitrary code.
- CVE-2001-1496 : Off-by-one buffer overflow in server allows remote attackers to cause a denial of service and possibly execute arbitrary code.
- CVE-2004-0342 : This is an interesting example that might not be an off-by-one.
- CVE-2001-0609 : An off-by-one enables a terminating null to be overwritten, which causes 2 strings to be merged and enable a format string.
- CVE-2002-1745 : Off-by-one error allows source code disclosure of files with 4 letter extensions that match an accepted 3-letter extension.
- CVE-2002-1816 : Off-by-one buffer overflow.
- CVE-2002-1721 : Off-by-one error causes an snprintf call to overwrite a critical internal variable with a null value.
- CVE-2003-0466 : Off-by-one error in function used in many products leads to a buffer overflow during pathname management, as demonstrated using multiple commands in an FTP server.
- CVE-2003-0625 : Off-by-one error allows read of sensitive memory via a malformed request.
- CVE-2006-4574 : Chain: security monitoring product has an off-by-one error that leads to unexpected length values, triggering an assertion.
For more examples, refer to CVE relations in the bottom box.
White Box Definitions None
Black Box Definitions None
|PLOVER || ||Off-by-one Error || |
|CERT C Secure Coding ||STR31-C ||Guarantee that storage for strings has sufficient space for
character data and the null terminator || |
|CERT C++ Secure Coding ||STR31-CPP ||Guarantee that storage for character arrays has sufficient
space for character data and the null terminator || |
- Halvar Flake .Third Generation Exploits. presentation at Black Hat Europe
- Steve Christey .Off-by-one errors: a brief explanation. Secprog and SC-L mailing list
- klog .The Frame Pointer Overwrite. Phrack Issue 55, Chapter 8. 1999-09-09.
- G. Hoglund G. McGraw .Exploiting Software: How to Break Code (The buffer overflow
chapter). Addison-Wesley. Published on February 2004.
- Michael Howard David LeBlanc John Viega .24 Deadly Sins of Software Security. McGraw-Hill. Section:'"Sin 5: Buffer Overruns." Page 89'. Published on 2010.
- Mark Dowd John McDonald Justin Schuh .The Art of Software Security Assessment 1st Edition. Addison Wesley. Section:'Chapter 5, "Off-by-One Errors", Page 180.'. Published on 2006.