Buffer Access Using Size of Source Buffer
Weakness ID: 806 (Weakness Variant)Status: Incomplete
+ Description

Description Summary

The software uses the size of a source buffer when reading from or writing to a destination buffer, which may cause it to access memory that is outside of the bounds of the buffer.

Extended Description

When the size of the destination is smaller than the size of the source, a buffer overflow could occur.

+ Time of Introduction
  • Implementation
+ Applicable Platforms


C: (Sometimes)

C++: (Sometimes)

+ Common Consequences

Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.


Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy.


When the consequence is arbitrary code execution, this can often be used to subvert any other security service.

+ Likelihood of Exploit

Medium to High

+ Potential Mitigations

Phase: Architecture and Design

Use an abstraction library to abstract away risky APIs. Examples include the Safe C String Library (SafeStr) by Viega, and the Strsafe.h library from Microsoft. This is not a complete solution, since many buffer overflows are not related to strings.

Phase: Build and Compilation

Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include StackGuard, ProPolice and the Microsoft Visual Studio /GS flag. This is not necessarily a complete solution, since these canary-based mechanisms only detect certain types of overflows. In addition, the result is still a denial of service, since the typical response is to exit the application.

Phase: Implementation

Programmers should adhere to the following rules when allocating and managing their applications memory: Double check that your buffer is as large as you specify. When using functions that accept a number of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the source buffer size, it may not NULL-terminate the string. Check buffer boundaries if calling this function in a loop and make sure you are not in danger of writing past the allocated space. Truncate all input strings to a reasonable length before passing them to the copy and concatenation functions

Phase: Operation

Use a feature like Address Space Layout Randomization (ASLR). This is not a complete solution. However, it forces the attacker to guess an unknown value that changes every program execution.

Phase: Operation

Use a CPU and operating system that offers Data Execution Protection (NX) or its equivalent. This is not a complete solution, since buffer overflows could be used to overwrite nearby variables to modify the software's state in dangerous ways.

Phases: Build and Compilation; Operation

Most mitigating technologies at the compiler or OS level to date address only a subset of buffer overflow problems and rarely provide complete protection against even that subset. It is good practice to implement strategies to increase the workload of an attacker, such as leaving the attacker to guess an unknown value that changes every program execution.

+ Weakness Ordinalities
(where the weakness is typically related to the presence of some other weaknesses)
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness BaseWeakness Base805Buffer Access with Incorrect Length Value
Development Concepts (primary)699
Research Concepts (primary)1000
+ Affected Resources
  • Memory
+ Causal Nature


+ References
Microsoft. "Using the Strsafe.h Functions". <http://msdn.microsoft.com/en-us/library/ms647466.aspx>.
Matt Messier and John Viega. "Safe C String Library v1.0.3". <http://www.zork.org/safestr/>.
Michael Howard. "Address Space Layout Randomization in Windows Vista". <http://blogs.msdn.com/michael_howard/archive/2006/05/26/address-space-layout-randomization-in-windows-vista.aspx>.
Arjan van de Ven. "Limiting buffer overflows with ExecShield". <http://www.redhat.com/magazine/009jul05/features/execshield/>.
"PaX". <http://en.wikipedia.org/wiki/PaX>.
+ Content History
Submission DateSubmitterOrganizationSource
2010-01-15MITREInternal CWE Team