The product does not properly protect an assumed-immutable element from being modified by an attacker.
This occurs when a particular input is critical enough to the functioning of the application that it should not be modifiable at all, but it is. Certain resources are often assumed to be immutable when they are not, such as hidden form fields in web applications, cookies, and reverse DNS lookups.

Primary

Resultant

Implementation

Architecture and Design

Integrity
Modify Application Data
Common data types that are attacked are environment variables, web application parameters, and HTTP headers.

Integrity
Unexpected State

Architecture and Design
Operation
Implementation
When the data is stored or transmitted through untrusted sources that could modify the data, implement integrity checks to detect unauthorized modification, or store/transmit the data in a trusted location that is free from external influence.

In the code excerpt below, an array returned by a Java method is modified despite the fact that arrays are mutable.

String[] colors = car.getAllPossibleColors();colors[0] = "Red";

CVE-2002-1757
Relies on $PHP_SELF variable for authentication.
https://www.cve.org/CVERecord?id=CVE-2002-1757

CVE-2005-1905
Gain privileges by modifying assumed-immutable code addresses that are accessed by a driver.
https://www.cve.org/CVERecord?id=CVE-2005-1905

Modification of Assumed-Immutable Data

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

MAID issues can be primary to many other weaknesses, and they are a major factor in languages that provide easy access to internal program constructs, such as PHP's register_globals and similar features. However, MAID issues can also be resultant from weaknesses that modify internal state; for example, a program might validate some data and store it in memory, but a buffer overflow could overwrite that validated data, leading to a change in program logic.
There are many examples where the MUTABILITY property is a major factor in a vulnerability.

PLOVER
2006-07-19
Draft 3
2006-07-19

Sean Eidemiller
Cigital
2008-07-01
added/updated demonstrative examples

Eric Dalci
Cigital
2008-07-01
updated Potential_Mitigations, Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Relationships, Other_Notes, Taxonomy_Mappings

CWE Content Team
MITRE
2009-07-27
updated Other_Notes

CWE Content Team
MITRE
2010-02-16
updated Potential_Mitigations

CWE Content Team
MITRE
2010-04-05
updated Related_Attack_Patterns

CWE Content Team
MITRE
2010-12-13
updated Related_Attack_Patterns

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2012-05-11
updated Relationships

CWE Content Team
MITRE
2013-02-21
updated Relationships

CWE Content Team
MITRE
2013-07-17
updated Relationships

CWE Content Team
MITRE
2014-02-18
updated Related_Attack_Patterns

CWE Content Team
MITRE
2014-06-23
updated Applicable_Platforms, Common_Consequences, Description, Other_Notes, Potential_Mitigations, Relationship_Notes, Theoretical_Notes, Time_of_Introduction

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2017-05-03
updated Related_Attack_Patterns

CWE Content Team
MITRE
2018-03-27
updated Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships

CWE Content Team
MITRE
2020-06-25
updated Relationships

CWE Content Team
MITRE
2020-12-10
updated Relationships

CWE Content Team
MITRE
2021-10-28
updated Relationships

CWE Content Team
MITRE
2023-01-31
updated Description

CWE Content Team
MITRE
2023-04-27
updated Relationships

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-04-03
4.17
2025-04-03
updated Relationships

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Applicable_Platforms, Weakness_Ordinalities