CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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ID

CWE-787: Out-of-bounds Write

Weakness ID: 787
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software writes data past the end, or before the beginning, of the intended buffer.
+ Extended Description
This typically occurs when the pointer or its index is incremented or decremented to a position beyond the bounds of the buffer or when pointer arithmetic results in a position outside of the valid memory location to name a few. This may result in corruption of sensitive information, a crash, or code execution among other things.
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
+ Relevant to the view "Weaknesses for Simplified Mapping of Published Vulnerabilities" (CWE-1003)
+ Relevant to the view "Development Concepts" (CWE-699)
+ Common Consequences

The table below 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.

ScopeImpactLikelihood
Integrity
Availability
Confidentiality

Technical Impact: Modify Memory; DoS: Crash, Exit, or Restart; Execute Unauthorized Code or Commands

+ Demonstrative Examples

Example 1

The following code attempts to save four different identification numbers into an array.

(bad code)
Example Language:
int id_sequence[3];

/* Populate the id array. */

id_sequence[0] = 123;
id_sequence[1] = 234;
id_sequence[2] = 345;
id_sequence[3] = 456;

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:
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).

+ Content History
Submissions
Submission DateSubmitterOrganization
2009-10-21CWE Content TeamMITRE
Modifications
Modification DateModifierOrganization
2010-02-16CWE Content TeamMITRE
updated Demonstrative_Examples
2010-09-27CWE Content TeamMITRE
updated Relationships
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2014-06-23CWE Content TeamMITRE
updated Demonstrative_Examples
2015-12-07CWE Content TeamMITRE
updated Relationships

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Page Last Updated: January 18, 2018