Incorrect Calculation of Multi-Byte String Length

Draft Base

Structure: Simple

Description

The product does not correctly calculate the length of strings that can contain wide or multi-byte characters.

Common Consequences 3

Scope: IntegrityConfidentialityAvailability

Impact: Execute Unauthorized Code or Commands

This weakness may lead to a buffer overflow. Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy. This can often be used to subvert any other security service.

Scope: AvailabilityConfidentiality

Impact: Read MemoryDoS: Crash, Exit, or RestartDoS: Resource Consumption (CPU)DoS: Resource Consumption (Memory)

Out of bounds memory access will very likely result in the corruption of relevant memory, and perhaps instructions, possibly leading to a crash. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.

Scope: Confidentiality

Impact: Read Memory

In the case of an out-of-bounds read, the attacker may have access to sensitive information. If the sensitive information contains system details, such as the current buffer's position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.

Detection Methods 1

Automated Static AnalysisHigh

Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)

Potential Mitigations 2

Phase: Implementation

Strategy: Input Validation

Always verify the length of the string unit character.

Phase: Implementation

Strategy: Libraries or Frameworks

Use length computing functions (e.g. strlen, wcslen, etc.) appropriately with their equivalent type (e.g.: byte, wchar_t, etc.)

Demonstrative Examples 1

The following example would be exploitable if any of the commented incorrect malloc calls were used.

Code Example:Bad
C
c

The output from the printf() statement would be:

Code Example:Result
bash

References 2

Writing Secure Code

Michael Howard and David LeBlanc

Microsoft Press

04-12-2002

https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223

ID: REF-7

The CLASP Application Security Process

Secure Software, Inc.

2005

https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf(2024-11-17)

ID: REF-18

Applicable Platforms

Languages:

C : UndeterminedC++ : Undetermined

Modes of Introduction

Implementation

Related Weaknesses

ChildOf:

Incorrect Calculation (CWE-682)

Taxonomy Mapping

CLASP
The CERT Oracle Secure Coding Standard for Java (2011)
Software Fault Patterns