CWE - CWE-121: Stack-based Buffer Overflow (4.18)

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CWE Glossary Definition

CWE-121: Stack-based Buffer Overflow

Weakness ID: 121

Vulnerability Mapping: ALLOWED This CWE ID may be used to map to real-world vulnerabilities
Abstraction: 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.

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Description

A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

Alternate Terms

Stack Overflow

"Stack Overflow" is often used to mean the same thing as stack-based buffer overflow, however it is also used on occasion to mean stack exhaustion, usually a result from an excessively recursive function call. Due to the ambiguity of the term, use of stack overflow to describe either circumstance is discouraged.

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; DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)	Scope: Availability Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
Modify Memory; Execute Unauthorized Code or Commands; Bypass Protection Mechanism	Scope: Integrity, Confidentiality, Availability, Access Control Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy.
Modify Memory; Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Other	Scope: Integrity, Confidentiality, Availability, 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
Operation; Build and Compilation	Strategy: Environment Hardening Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail. Effectiveness: Defense in Depth Note: This is not necessarily a complete solution, since these 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.
Architecture and Design	Use an abstraction library to abstract away risky APIs. Not a complete solution.
Implementation	Implement and perform bounds checking on input.
Implementation	Do not use dangerous functions such as gets. Use safer, equivalent functions which check for boundary errors.
Operation; Build and Compilation	Strategy: Environment Hardening Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code. Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking. For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335]. Effectiveness: Defense in Depth Note: These techniques do not provide a complete solution. For instance, exploits frequently use a bug that discloses memory addresses in order to maximize reliability of code execution [REF-1337]. It has also been shown that a side-channel attack can bypass ASLR [REF-1333]

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
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.	788	Access of Memory Location After End of Buffer

Background Details

There are generally several security-critical data on an execution stack that can lead to arbitrary code execution. The most prominent is the stored return address, the memory address at which execution should continue once the current function is finished executing. The attacker can overwrite this value with some memory address to which the attacker also has write access, into which they place arbitrary code to be run with the full privileges of the vulnerable program. Alternately, the attacker can supply the address of an important call, for instance the POSIX system() call, leaving arguments to the call on the stack. This is often called a return into libc exploit, since the attacker generally forces the program to jump at return time into an interesting routine in the C standard library (libc). Other important data commonly on the stack include the stack pointer and frame pointer, two values that indicate offsets for computing memory addresses. Modifying those values can often be leveraged into a "write-what-where" condition.

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 (Often Prevalent)

C++ (Often Prevalent)

Likelihood Of Exploit

High

Demonstrative Examples

Example 1

While buffer overflow examples can be rather complex, it is possible to have very simple, yet still exploitable, stack-based buffer overflows:

(bad code)

Example Language: C

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

char buf[BUFSIZE];
strcpy(buf, argv[1]);

}

The buffer size is fixed, but there is no guarantee the string in argv[1] will not exceed this size and cause an overflow.

Example 2

This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer.

(bad code)

Example Language: C

void host_lookup(char *user_supplied_addr){

struct hostent *hp;
in_addr_t *addr;
char hostname[64];
in_addr_t inet_addr(const char *cp);

/*routine that ensures user_supplied_addr is in the right format for conversion */

validate_addr_form(user_supplied_addr);
addr = inet_addr(user_supplied_addr);
hp = gethostbyaddr( addr, sizeof(struct in_addr), AF_INET);
strcpy(hostname, hp->h_name);

}

This function allocates a buffer of 64 bytes to store the hostname, however there is no guarantee that the hostname will not be larger than 64 bytes. If an attacker specifies an address which resolves to a very large hostname, then the function may overwrite sensitive data or even relinquish control flow to the attacker.

Note that this example also contains an unchecked return value (CWE-252) that can lead to a NULL pointer dereference (CWE-476).

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-2021-35395	Stack-based buffer overflows in SFK for wifi chipset used for IoT/embedded devices, as exploited in the wild per CISA KEV.

Weakness Ordinalities

Ordinality	Description
Primary	(where the weakness exists independent of other weaknesses)

Detection Methods

Method	Details
Fuzzing	Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues. Effectiveness: High
Automated Static Analysis	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.) Effectiveness: High

Method

Details

Fuzzing

Fuzz testing (fuzzing) is a powerful technique for generating large numbers of diverse inputs - either randomly or algorithmically - and dynamically invoking the code with those inputs. Even with random inputs, it is often capable of generating unexpected results such as crashes, memory corruption, or resource consumption. Fuzzing effectively produces repeatable test cases that clearly indicate bugs, which helps developers to diagnose the issues.

Effectiveness: High

Automated Static Analysis

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.)

Effectiveness: High

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.	1365	ICS Communications: Unreliability
MemberOf	CategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.	1366	ICS Communications: Frail Security in Protocols
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 Variant 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.

Notes

Other

Stack-based buffer overflows can instantiate in return address overwrites, stack pointer overwrites or frame pointer overwrites. They can also be considered function pointer overwrites, array indexer overwrites or write-what-where condition, etc.

Taxonomy Mappings

Mapped Taxonomy Name	Node ID	Fit	Mapped Node Name
CLASP	Stack overflow
Software Fault Patterns	SFP8	Faulty Buffer Access
CERT C Secure Coding	ARR38-C	Imprecise	Guarantee that library functions do not form invalid pointers
CERT C Secure Coding	STR31-C	CWE More Specific	Guarantee that storage for strings has sufficient space for character data and the null terminator

References

[REF-1029] Aleph One. "Smashing The Stack For Fun And Profit". Phrack. 1996年11月08日.
<https://phrack.org/issues/49/14.html>.

[REF-7] Michael Howard and David LeBlanc. "Writing Secure Code". Chapter 5, "Stack Overruns" Page 129. 2nd Edition. Microsoft Press. 2002年12月04日.
<https://www.microsoftpressstore.com/store/writing-secure-code-9780735617223>.

[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-62] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 3, "Nonexecutable Stack", Page 76. 1st Edition. Addison Wesley. 2006.

[REF-62] Mark Dowd, John McDonald and Justin Schuh. "The Art of Software Security Assessment". Chapter 5, "Protection Mechanisms", Page 189. 1st Edition. Addison Wesley. 2006.

[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)

[REF-58] Michael Howard. "Address Space Layout Randomization in Windows Vista".
<https://learn.microsoft.com/en-us/archive/blogs/michael_howard/address-space-layout-randomization-in-windows-vista>. (URL validated: 2023年04月07日)

[REF-60] "PaX".
<https://en.wikipedia.org/wiki/Executable_space_protection#PaX>. (URL validated: 2023年04月07日)

[REF-64] Grant Murphy. "Position Independent Executables (PIE)". Red Hat. 2012年11月28日.
<https://www.redhat.com/en/blog/position-independent-executables-pie>. (URL validated: 2023年04月07日)

[REF-1332] John Richard Moser. "Prelink and address space randomization". 2006年07月05日.
<https://lwn.net/Articles/190139/>. (URL validated: 2023年04月26日)

[REF-1333] Dmitry Evtyushkin, Dmitry Ponomarev, Nael Abu-Ghazaleh. "Jump Over ASLR: Attacking Branch Predictors to Bypass ASLR". 2016.
<http://www.cs.ucr.edu/~nael/pubs/micro16.pdf>. (URL validated: 2023年04月26日)

[REF-1334] D3FEND. "Stack Frame Canary Validation (D3-SFCV)". 2023.
<https://d3fend.mitre.org/technique/d3f:StackFrameCanaryValidation/>. (URL validated: 2023年04月26日)

[REF-1335] D3FEND. "Segment Address Offset Randomization (D3-SAOR)". 2023.
<https://d3fend.mitre.org/technique/d3f:SegmentAddressOffsetRandomization/>. (URL validated: 2023年04月26日)

[REF-1337] Alexander Sotirov and Mark Dowd. "Bypassing Browser Memory Protections: Setting back browser security by 10 years". Memory information leaks. 2008.
<https://www.blackhat.com/presentations/bh-usa-08/Sotirov_Dowd/bh08-sotirov-dowd.pdf>. (URL validated: 2023年04月26日)

[REF-1477] Cybersecurity and Infrastructure Security Agency. "Secure by Design Alert: Eliminating Buffer Overflow Vulnerabilities". 2025年02月12日.
<https://www.cisa.gov/resources-tools/resources/secure-design-alert-eliminating-buffer-overflow-vulnerabilities>. (URL validated: 2025年07月18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, References
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 Applicable_Platforms
2023年06月29日	CWE Content Team	MITRE
2023年06月29日	updated Mapping_Notes, Relationships
2023年04月27日	CWE Content Team	MITRE
2023年04月27日	updated Detection_Factors, Potential_Mitigations, References, Relationships, Time_of_Introduction
2022年06月28日	CWE Content Team	MITRE
2022年06月28日	updated Observed_Examples
2021年07月20日	CWE Content Team	MITRE
2021年07月20日	updated Demonstrative_Examples
2021年03月15日	CWE Content Team	MITRE
2021年03月15日	updated Demonstrative_Examples, References
2020年06月25日	CWE Content Team	MITRE
2020年06月25日	updated Common_Consequences
2020年02月24日	CWE Content Team	MITRE
2020年02月24日	updated Relationships
2019年09月19日	CWE Content Team	MITRE
2019年09月19日	updated References
2019年01月03日	CWE Content Team	MITRE
2019年01月03日	updated Relationships
2018年03月27日	CWE Content Team	MITRE
2018年03月27日	updated References
2017年11月08日	CWE Content Team	MITRE
2017年11月08日	updated Background_Details, Causal_Nature, Likelihood_of_Exploit, References, Relationships, Taxonomy_Mappings, White_Box_Definitions
2014年07月30日	CWE Content Team	MITRE
2014年07月30日	updated Relationships, Taxonomy_Mappings
2012年10月30日	CWE Content Team	MITRE
2012年10月30日	updated Demonstrative_Examples, Potential_Mitigations
2012年05月11日	CWE Content Team	MITRE
2012年05月11日	updated Demonstrative_Examples, References, Relationships
2011年06月01日	CWE Content Team	MITRE
2011年06月01日	updated Common_Consequences
2010年02月16日	CWE Content Team	MITRE
2010年02月16日	updated References
2009年10月29日	CWE Content Team	MITRE
2009年10月29日	updated Relationships
2009年07月27日	CWE Content Team	MITRE
2009年07月27日	updated Potential_Mitigations, White_Box_Definitions
2009年07月17日	KDM Analytics
2009年07月17日	Improved the White_Box_Definition
2009年01月12日	CWE Content Team	MITRE
2009年01月12日	updated Common_Consequences, Relationships
2008年09月08日	CWE Content Team	MITRE
2008年09月08日	updated Alternate_Terms, Applicable_Platforms, Background_Details, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities
2008年08月01日	KDM Analytics
2008年08月01日	added/updated white box definitions
2008年07月01日	Eric Dalci	Cigital
2008年07月01日	updated Potential_Mitigations, Time_of_Introduction

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Page Last Updated: September 09, 2025

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