CWE - CWE-123: Write-what-where Condition (4.18)

Home > CWE List > CWE-123: Write-what-where Condition (4.18)

CWE Glossary Definition

CWE-123: Write-what-where Condition

Weakness ID: 123

Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.

View customized information:

For users who are interested in more notional aspects of a weakness. Example: educators, technical writers, and project/program managers. For users who are concerned with the practical application and details about the nature of a weakness and how to prevent it from happening. Example: tool developers, security researchers, pen-testers, incident response analysts. For users who are mapping an issue to CWE/CAPEC IDs, i.e., finding the most appropriate CWE for a specific issue (e.g., a CVE record). Example: tool developers, security researchers. For users who wish to see all available information for the CWE/CAPEC entry. For users who want to customize what details are displayed.

Edit Custom Filter

Description

Any condition where the attacker has the ability to write an arbitrary value to an arbitrary location, often as the result of a buffer overflow.

Common Consequences

Section HelpThis table 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.

Impact	Details
Modify Memory; Execute Unauthorized Code or Commands; Gain Privileges or Assume Identity; DoS: Crash, Exit, or Restart; Bypass Protection Mechanism	Scope: Integrity, Confidentiality, Availability, Access Control Clearly, write-what-where conditions can be used to write data to areas of memory outside the scope of a policy. Also, they almost invariably can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy. If the attacker can overwrite a pointer's worth of memory (usually 32 or 64 bits), they can redirect a function pointer to their own malicious code. Even when the attacker can only modify a single byte arbitrary code execution can be possible. Sometimes this is because the same problem can be exploited repeatedly to the same effect. Other times it is because the attacker can overwrite security-critical application-specific data -- such as a flag indicating whether the user is an administrator.
DoS: Crash, Exit, or Restart; Modify Memory	Scope: Integrity, Availability Many memory accesses can lead to program termination, such as when writing to addresses that are invalid for the current process.
Bypass Protection Mechanism; Other	Scope: Access Control, Other When the consequence is arbitrary code execution, this can often be used to subvert any other security service.

Potential Mitigations

Phase(s)	Mitigation
Architecture and Design	Strategy: Language Selection Use a language that provides appropriate memory abstractions.
Operation	Use OS-level preventative functionality integrated after the fact. Not a complete solution.

Relationships

Section Help This table 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" (View-1000)

Nature	Type	ID	Name
ChildOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	787	Out-of-bounds Write
PeerOf	Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.	415	Double Free
CanFollow	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	120	Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
CanFollow	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	134	Use of Externally-Controlled Format String
CanFollow	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	364	Signal Handler Race Condition
CanFollow	Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.	416	Use After Free
CanFollow	Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.	479	Signal Handler Use of a Non-reentrant Function
CanFollow	Variant Variant - a weakness that is linked to a certain type of product, typically involving a specific language or technology. More specific than a Base weakness. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource.	590	Free of Memory not on the Heap

Relevant to the view "CISQ Quality Measures (2020)" (View-1305)

Nature	Type	ID	Name
ChildOf	Base Base - a weakness that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource.	787	Out-of-bounds Write

Relevant to the view "CISQ Data Protection Measures" (View-1340)

Nature	Type	ID	Name
ChildOf	Class Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More specific than a Pillar Weakness, but more general than a Base Weakness. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource.	119	Improper Restriction of Operations within the Bounds of a Memory Buffer

Modes Of Introduction

Section HelpThe different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

Phase	Note
Implementation

Applicable Platforms

Section HelpThis listing shows possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.

Languages

C (Undetermined Prevalence)

C++ (Undetermined Prevalence)

Likelihood Of Exploit

High

Demonstrative Examples

Example 1

The classic example of a write-what-where condition occurs when the accounting information for memory allocations is overwritten in a particular fashion. Here is an example of potentially vulnerable code:

(bad code)

Example Language: C

#define BUFSIZE 256
int main(int argc, char **argv) {

char *buf1 = (char *) malloc(BUFSIZE);
char *buf2 = (char *) malloc(BUFSIZE);
strcpy(buf1, argv[1]);
free(buf2);

}

Vulnerability in this case is dependent on memory layout. The call to strcpy() can be used to write past the end of buf1, and, with a typical layout, can overwrite the accounting information that the system keeps for buf2 when it is allocated. Note that if the allocation header for buf2 can be overwritten, buf2 itself can be overwritten as well.

The allocation header will generally keep a linked list of memory "chunks". Particularly, there may be a "previous" chunk and a "next" chunk. Here, the previous chunk for buf2 will probably be buf1, and the next chunk may be null. When the free() occurs, most memory allocators will rewrite the linked list using data from buf2. Particularly, the "next" chunk for buf1 will be updated and the "previous" chunk for any subsequent chunk will be updated. The attacker can insert a memory address for the "next" chunk and a value to write into that memory address for the "previous" chunk.

This could be used to overwrite a function pointer that gets dereferenced later, replacing it with a memory address that the attacker has legitimate access to, where they have placed malicious code, resulting in arbitrary code execution.

Selected Observed Examples

Note: this is a curated list of examples for users to understand the variety of ways in which this weakness can be introduced. It is not a complete list of all CVEs that are related to this CWE entry.

Reference	Description
CVE-2019-19911	Chain: Python library does not limit the resources used to process images that specify a very large number of bands (CWE-1284), leading to excessive memory consumption (CWE-789) or an integer overflow (CWE-190).
CVE-2022-0545	Chain: 3D renderer has an integer overflow (CWE-190) leading to write-what-where condition (CWE-123) using a crafted image.

Weakness Ordinalities

Ordinality	Description
Resultant	(where the weakness is typically related to the presence of some other weaknesses)

Functional Areas

Memory Management

Affected Resources

Memory

Memberships

Section HelpThis MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.

Nature	Type	ID	Name
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	970	SFP Secondary Cluster: Faulty Buffer Access
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1160	SEI CERT C Coding Standard - Guidelines 06. Arrays (ARR)
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1161	SEI CERT C Coding Standard - Guidelines 07. Characters and Strings (STR)
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1399	Comprehensive Categorization: Memory Safety

Vulnerability Mapping Notes

Usage ALLOWED

(this CWE ID may be used to map to real-world vulnerabilities)

Reason Acceptable-Use

Rationale

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.

Comments

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.

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Fit	Mapped Node Name
CLASP	Write-what-where condition
CERT C Secure Coding	ARR30-C	Imprecise	Do not form or use out-of-bounds pointers or array subscripts
CERT C Secure Coding	ARR38-C	Imprecise	Guarantee that library functions do not form invalid pointers
CERT C Secure Coding	STR31-C	Imprecise	Guarantee that storage for strings has sufficient space for character data and the null terminator
CERT C Secure Coding	STR32-C	Imprecise	Do not pass a non-null-terminated character sequence to a library function that expects a string
Software Fault Patterns	SFP8	Faulty Buffer Access

References

[REF-44] Michael Howard, David LeBlanc and John Viega. "24 Deadly Sins of Software Security". "Sin 5: Buffer Overruns." Page 89. McGraw-Hill. 2010.

[REF-18] Secure Software, Inc.. "The CLASP Application Security Process". 2005.
<https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf>. (URL validated: 2024年11月17日)

Content History

Submissions
Submission Date	Submitter	Organization
2006年07月19日 (CWE Draft 3, 2006年07月19日)	CLASP
2006年07月19日 (CWE Draft 3, 2006年07月19日)
Modifications
Modification Date	Modifier	Organization
2025年09月09日 (CWE 4.18, 2025年09月09日)	CWE Content Team	MITRE
2025年09月09日 (CWE 4.18, 2025年09月09日)	updated Affected_Resources, Functional_Areas, Observed_Examples
2025年04月03日 (CWE 4.17, 2025年04月03日)	CWE Content Team	MITRE
2025年04月03日 (CWE 4.17, 2025年04月03日)	updated Relationships
2023年10月26日	CWE Content Team	MITRE
2023年10月26日	updated Observed_Examples
2023年06月29日	CWE Content Team	MITRE
2023年06月29日	updated Mapping_Notes
2023年04月27日	CWE Content Team	MITRE
2023年04月27日	updated Relationships
2022年10月13日	CWE Content Team	MITRE
2022年10月13日	updated Relationships, Taxonomy_Mappings
2021年03月15日	CWE Content Team	MITRE
2021年03月15日	updated References
2020年12月10日	CWE Content Team	MITRE
2020年12月10日	updated Relationships
2020年08月20日	CWE Content Team	MITRE
2020年08月20日	updated Relationships
2020年02月24日	CWE Content Team	MITRE
2020年02月24日	updated Relationships, Taxonomy_Mappings
2019年09月19日	CWE Content Team	MITRE
2019年09月19日	updated Relationships
2019年06月20日	CWE Content Team	MITRE
2019年06月20日	updated Relationships
2019年01月03日	CWE Content Team	MITRE
2019年01月03日	updated Relationships
2017年11月08日	CWE Content Team	MITRE
2017年11月08日	updated Causal_Nature, Common_Consequences, Demonstrative_Examples, Taxonomy_Mappings
2015年12月07日	CWE Content Team	MITRE
2015年12月07日	updated Relationships
2014年07月30日	CWE Content Team	MITRE
2014年07月30日	updated Relationships, Taxonomy_Mappings
2013年02月21日	CWE Content Team	MITRE
2013年02月21日	updated Potential_Mitigations
2012年10月30日	CWE Content Team	MITRE
2012年10月30日	updated Demonstrative_Examples
2012年05月11日	CWE Content Team	MITRE
2012年05月11日	updated Common_Consequences, References, Relationships
2011年06月01日	CWE Content Team	MITRE
2011年06月01日	updated Common_Consequences
2010年12月13日	CWE Content Team	MITRE
2010年12月13日	updated Relationships
2009年05月27日	CWE Content Team	MITRE
2009年05月27日	updated Relationships
2009年01月12日	CWE Content Team	MITRE
2009年01月12日	updated Common_Consequences
2008年11月24日	CWE Content Team	MITRE
2008年11月24日	updated Common_Consequences, Other_Notes
2008年09月08日	CWE Content Team	MITRE
2008年09月08日	updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities
2008年07月01日	Eric Dalci	Cigital
2008年07月01日	updated Time_of_Introduction

More information is available — Please edit the custom filter or select a different filter.

Page Last Updated: September 09, 2025

MITRE

Use of the Common Weakness Enumeration (CWE™) and the associated references from this website are subject to the Terms of Use. CWE is sponsored by the U.S. Department of Homeland Security (DHS) Cybersecurity and Infrastructure Security Agency (CISA) and managed by the Homeland Security Systems Engineering and Development Institute (HSSEDI) which is operated by The MITRE Corporation (MITRE). Copyright © 2006–2025, The MITRE Corporation. CWE, CWSS, CWRAF, and the CWE logo are trademarks of The MITRE Corporation.

HSSEDI