CWE

Incorrect Calculation of Multi-Byte String Length

ID: 135		Date: (C)2012-05-14   (M)2022-10-10
Type: weakness		Status: DRAFT
Abstraction Type: Base

Description

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

Applicable Platforms
Language: C
Language: C++

Time Of Introduction

• Implementation

Common Consequences

Scope	Technical Impact	Notes
Integrity Confidentiality Availability	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.
Availability Confidentiality	Read memory DoS: crash / exit / restart DoS: 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.
Confidentiality	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 buffers position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.

Detection Methods
None

Potential Mitigations

Phase	Strategy	Description	Effectiveness	Notes
Implementation	Input Validation	Always verify the length of the string unit character.
Implementation	Libraries or Frameworks	Use length computing functions (e.g. strlen, wcslen, etc.) appropriately with their equivalent type (e.g.: byte, wchar_t, etc.)

Relationships

Related CWE	Type	View	Chain
CWE-135 ChildOf CWE-890	Category	CWE-888

Demonstrative Examples   (Details)

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

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

Taxynomy	Id	Name	Fit
CLASP		Improper string length checking
CERT C Secure Coding	STR33-C	Size wide character strings correctly
CERT Java Secure Coding	FIO10-J	Ensure the array is filled when using read() to fill an array

References:

1. M. Howard D. LeBlanc .Writing Secure Code 2nd Edition. Microsoft. Section:'Chapter 5, "Unicode and ANSI Buffer Size Mismatches" Page 153'. Published on 2002.