The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

Primary

Resultant

Certain languages allow direct addressing of memory locations and do not automatically ensure that these locations are valid for the memory buffer that is being referenced.

Buffer Overflow
This term has many different meanings to different audiences. From a CWE mapping perspective, this term should be avoided where possible. Some researchers, developers, and tools intend for it to mean "write past the end of a buffer," whereas others use the same term to mean "any read or write outside the boundaries of a buffer, whether before the beginning of the buffer or after the end of the buffer." Others could mean "any action after the end of a buffer, whether it is a read or write." Since the term is commonly used for exploitation and for vulnerabilities, it further confuses things.

buffer overrun
Some prominent vendors and researchers use the term "buffer overrun," but most people use "buffer overflow." See the alternate term for "buffer overflow" for context.

memory safety
Generally used for techniques that avoid weaknesses related to memory access, such as those identified by CWE-119 and its descendants. However, the term is not formal, and there is likely disagreement between practitioners as to which weaknesses are implicitly covered by the "memory safety" term.

Implementation

High

Integrity
Confidentiality
Availability
Execute Unauthorized Code or Commands
Modify Memory
If the memory accessible by the attacker can be effectively controlled, it may be possible to execute arbitrary code, as with a standard buffer overflow. If the attacker can overwrite a pointer's worth of memory (usually 32 or 64 bits), they can alter the intended control flow by redirecting 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.

Availability
Confidentiality
Read Memory
DoS: Crash, Exit, or 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 buffer's position in memory, this knowledge can be used to craft further attacks, possibly with more severe consequences.

Automated Static Analysis

This weakness can often be detected using automated static analysis tools. Many modern tools use data flow analysis or constraint-based techniques to minimize the number of false positives.
Automated static analysis generally does not account for environmental considerations when reporting out-of-bounds memory operations. This can make it difficult for users to determine which warnings should be investigated first. For example, an analysis tool might report buffer overflows that originate from command line arguments in a program that is not expected to run with setuid or other special privileges.

High
Detection techniques for buffer-related errors are more mature than for most other weakness types.

Automated Dynamic Analysis
This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.

Automated Dynamic Analysis
Use tools that are integrated during
compilation to insert runtime error-checking mechanisms
related to memory safety errors, such as AddressSanitizer
(ASan) for C/C++ [REF-1518].
Moderate
Crafted inputs are necessary to
reach the code containing the error, such as generated
by fuzzers. Also, these tools may reduce performance,
and they only report the error condition - not the
original mistake that led to the
error.

Automated Static Analysis - Binary or Bytecode

According to SOAR [REF-1479], the following detection techniques may be useful:

Cost effective for partial coverage:

Binary / Bytecode Quality Analysis
Bytecode Weakness Analysis - including disassembler + source code weakness analysis
Binary Weakness Analysis - including disassembler + source code weakness analysis

SOAR Partial

Manual Static Analysis - Binary or Bytecode

According to SOAR [REF-1479], the following detection techniques may be useful:

Cost effective for partial coverage:

Binary / Bytecode disassembler - then use manual analysis for vulnerabilities & anomalies

SOAR Partial

Dynamic Analysis with Automated Results Interpretation

According to SOAR [REF-1479], the following detection techniques may be useful:

Cost effective for partial coverage:

Web Application Scanner
Web Services Scanner
Database Scanners

SOAR Partial

Dynamic Analysis with Manual Results Interpretation

According to SOAR [REF-1479], the following detection techniques may be useful:

Cost effective for partial coverage:

Fuzz Tester
Framework-based Fuzzer

SOAR Partial

Manual Static Analysis - Source Code

According to SOAR [REF-1479], the following detection techniques may be useful:

Cost effective for partial coverage:

Focused Manual Spotcheck - Focused manual analysis of source
Manual Source Code Review (not inspections)

SOAR Partial

Automated Static Analysis - Source Code

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Source code Weakness Analyzer
Context-configured Source Code Weakness Analyzer

Cost effective for partial coverage:

Source Code Quality Analyzer

High

Architecture or Design Review

According to SOAR [REF-1479], the following detection techniques may be useful:

Highly cost effective:

Formal Methods / Correct-By-Construction

Cost effective for partial coverage:

Inspection (IEEE 1028 standard) (can apply to requirements, design, source code, etc.)

High

Requirements
Language Selection

Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.
Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

Architecture and Design
Libraries or Frameworks

Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.

This is not a complete solution, since many buffer overflows are not related to strings.

Operation
Build and Compilation
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.

Defense in Depth

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.

Implementation

Consider adhering to the following rules when allocating and managing an application's memory:

Double check that the buffer is as large as specified.
When using functions that accept a number of bytes to copy, such as strncpy(), be aware that if the destination buffer size is equal to the source buffer size, it may not NULL-terminate the string.
Check buffer boundaries if accessing the buffer in a loop and make sure there is no danger of writing past the allocated space.
If necessary, truncate all input strings to a reasonable length before passing them to the copy and concatenation functions.

Operation
Build and Compilation
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].

Defense in Depth
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].

Operation
Environment Hardening

Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.
For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].

Defense in Depth
This is not a complete solution, since buffer overflows could be used to overwrite nearby variables to modify the software's state in dangerous ways. In addition, it cannot be used in cases in which self-modifying code is required. Finally, an attack could still cause a denial of service, since the typical response is to exit the application.

Implementation
Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.
Moderate
This approach is still susceptible to calculation errors, including issues such as off-by-one errors (CWE-193) and incorrectly calculating buffer lengths (CWE-131).

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.

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).

This example applies an encoding procedure to an input string and stores it into a buffer.

char * copy_input(char *user_supplied_string){
int i, dst_index;char *dst_buf = (char*)malloc(4*sizeof(char) * MAX_SIZE);if ( MAX_SIZE <= strlen(user_supplied_string) ){die("user string too long, die evil hacker!");}dst_index = 0;for ( i = 0; i < strlen(user_supplied_string); i++ ){
if( '&' == user_supplied_string[i] ){dst_buf[dst_index++] = '&';dst_buf[dst_index++] = 'a';dst_buf[dst_index++] = 'm';dst_buf[dst_index++] = 'p';dst_buf[dst_index++] = ';';}else if ('<' == user_supplied_string[i] ){
/* encode to &lt; */

}else dst_buf[dst_index++] = user_supplied_string[i];
}return dst_buf;
}

The programmer attempts to encode the ampersand character in the user-controlled string, however the length of the string is validated before the encoding procedure is applied. Furthermore, the programmer assumes encoding expansion will only expand a given character by a factor of 4, while the encoding of the ampersand expands by 5. As a result, when the encoding procedure expands the string it is possible to overflow the destination buffer if the attacker provides a string of many ampersands.

The following example asks a user for an offset into an array to select an item.

int main (int argc, char **argv) {char *items[] = {"boat", "car", "truck", "train"};int index = GetUntrustedOffset();printf("You selected %s\n", items[index-1]);}

The programmer allows the user to specify which element in the list to select, however an attacker can provide an out-of-bounds offset, resulting in a buffer over-read (CWE-126).

In the following code, the method retrieves a value from an array at a specific array index location that is given as an input parameter to the method

int getValueFromArray(int *array, int len, int index) {

int value;

// check that the array index is less than the maximum

// length of the array
if (index < len) {

// get the value at the specified index of the array
value = array[index];
}
// if array index is invalid then output error message

// and return value indicating error
else {printf("Value is: %d\n", array[index]);value = -1;}
return value;
}

However, this method only verifies that the given array index is less than the maximum length of the array but does not check for the minimum value (CWE-839). This will allow a negative value to be accepted as the input array index, which will result in reading data before the beginning of the buffer (CWE-127) and may allow access to sensitive memory. The input array index should be checked to verify that is within the maximum and minimum range required for the array (CWE-129). In this example the if statement should be modified to include a minimum range check, as shown below.

...

// check that the array index is within the correct

// range of values for the array
if (index >= 0 && index < len) {
...

Windows provides the _mbs family of functions to perform various operations on multibyte strings. When these functions are passed a malformed multibyte string, such as a string containing a valid leading byte followed by a single null byte, they can read or write past the end of the string buffer causing a buffer overflow. The following functions all pose a risk of buffer overflow: _mbsinc _mbsdec _mbsncat _mbsncpy _mbsnextc _mbsnset _mbsrev _mbsset _mbsstr _mbstok _mbccpy _mbslen

CVE-2021-22991
Incorrect URI normalization in application traffic product leads to buffer overflow, as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2021-22991

CVE-2020-29557
Buffer overflow in Wi-Fi router web interface, as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2020-29557

CVE-2009-2550
Classic stack-based buffer overflow in media player using a long entry in a playlist
https://www.cve.org/CVERecord?id=CVE-2009-2550

CVE-2009-2403
Heap-based buffer overflow in media player using a long entry in a playlist
https://www.cve.org/CVERecord?id=CVE-2009-2403

CVE-2009-0689
large precision value in a format string triggers overflow
https://www.cve.org/CVERecord?id=CVE-2009-0689

CVE-2009-0690
negative offset value leads to out-of-bounds read
https://www.cve.org/CVERecord?id=CVE-2009-0690

CVE-2009-1532
malformed inputs cause accesses of uninitialized or previously-deleted objects, leading to memory corruption
https://www.cve.org/CVERecord?id=CVE-2009-1532

CVE-2009-1528
chain: lack of synchronization leads to memory corruption
https://www.cve.org/CVERecord?id=CVE-2009-1528

CVE-2021-29529
Chain: machine-learning product can have a heap-based
buffer overflow (CWE-122) when some integer-oriented bounds are
calculated by using ceiling() and floor() on floating point values
(CWE-1339)
https://www.cve.org/CVERecord?id=CVE-2021-29529

CVE-2009-0558
attacker-controlled array index leads to code execution
https://www.cve.org/CVERecord?id=CVE-2009-0558

CVE-2009-0269
chain: -1 value from a function call was intended to indicate an error, but is used as an array index instead.
https://www.cve.org/CVERecord?id=CVE-2009-0269

CVE-2009-0566
chain: incorrect calculations lead to incorrect pointer dereference and memory corruption
https://www.cve.org/CVERecord?id=CVE-2009-0566

CVE-2009-1350
product accepts crafted messages that lead to a dereference of an arbitrary pointer
https://www.cve.org/CVERecord?id=CVE-2009-1350

CVE-2009-0191
chain: malformed input causes dereference of uninitialized memory
https://www.cve.org/CVERecord?id=CVE-2009-0191

CVE-2008-4113
OS kernel trusts userland-supplied length value, allowing reading of sensitive information
https://www.cve.org/CVERecord?id=CVE-2008-4113

CVE-2005-1513
Chain: integer overflow in securely-coded mail program leads to buffer overflow. In 2005, this was regarded as unrealistic to exploit, but in 2020, it was rediscovered to be easier to exploit due to evolutions of the technology.
https://www.cve.org/CVERecord?id=CVE-2005-1513

CVE-2003-0542
buffer overflow involving a regular expression with a large number of captures
https://www.cve.org/CVERecord?id=CVE-2003-0542

CVE-2017-1000121
chain: unchecked message size metadata allows integer overflow (CWE-190) leading to buffer overflow (CWE-119).
https://www.cve.org/CVERecord?id=CVE-2017-1000121

Memory Management

Memory

A5
Buffer Overflows
Exact

ARR00-C
Understand how arrays work

ARR30-C
Do not form or use out-of-bounds pointers or array subscripts
CWE More Abstract

ARR38-C
Guarantee that library functions do not form invalid pointers
CWE More Abstract

ENV01-C
Do not make assumptions about the size of an environment variable

EXP39-C
Do not access a variable through a pointer of an incompatible type
Imprecise

FIO37-C
Do not assume character data has been read

STR31-C
Guarantee that storage for strings has sufficient space for character data and the null terminator
CWE More Abstract

STR32-C
Do not pass a non-null-terminated character sequence to a library function that expects a string
CWE More Abstract

7
Buffer Overflow

SFP8
Faulty Buffer Access

Discouraged
CWE-119 is commonly misused in low-information vulnerability reports when lower-level CWEs could be used instead, or when more details about the vulnerability are available.
Look at CWE-119's children and consider mapping to CWEs such as CWE-787: Out-of-bounds Write, CWE-125: Out-of-bounds Read, or others.

It is possible in any programming languages without memory management support to attempt an operation outside of the bounds of a memory buffer, but the consequences will vary widely depending on the language, platform, and chip architecture.

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

Eric Dalci
Cigital
2008-07-01
updated Time_of_Introduction

Veracode
2008-08-15
Suggested OWASP Top Ten 2004 mapping

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

CWE Content Team
MITRE
2008-10-14
updated Relationships

CWE Content Team
MITRE
2008-11-24
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2009-01-12
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Likelihood_of_Exploit, Name, Potential_Mitigations, References, Relationships

CWE Content Team
MITRE
2009-03-10
updated Potential_Mitigations

CWE Content Team
MITRE
2009-05-27
updated Demonstrative_Examples

CWE Content Team
MITRE
2009-07-27
updated Observed_Examples

CWE Content Team
MITRE
2009-10-29
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Description, Relationships, Time_of_Introduction

CWE Content Team
MITRE
2009-12-28
updated Common_Consequences, Demonstrative_Examples, Detection_Factors, Observed_Examples

CWE Content Team
MITRE
2010-02-16
updated Alternate_Terms, Applicable_Platforms, Demonstrative_Examples, Detection_Factors, Potential_Mitigations, References, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2010-06-21
updated Potential_Mitigations

CWE Content Team
MITRE
2010-09-27
updated Potential_Mitigations, Relationships

CWE Content Team
MITRE
2010-12-13
updated Name

CWE Content Team
MITRE
2011-03-29
updated Relationships

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences, Relationships

CWE Content Team
MITRE
2011-09-13
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-05-11
updated Demonstrative_Examples, Potential_Mitigations, References, Relationships

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2013-02-21
updated Demonstrative_Examples

CWE Content Team
MITRE
2014-02-18
updated Potential_Mitigations, References

CWE Content Team
MITRE
2014-07-30
updated Detection_Factors, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2015-12-07
updated Relationships

CWE Content Team
MITRE
2017-01-19
updated Relationships

CWE Content Team
MITRE
2017-05-03
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Applicable_Platforms, Common_Consequences, Demonstrative_Examples, Observed_Examples, References, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2018-03-27
updated References

CWE Content Team
MITRE
2019-01-03
updated Relationships

CWE Content Team
MITRE
2019-06-20
updated Related_Attack_Patterns, Relationships

CWE Content Team
MITRE
2019-09-19
updated References, Relationships

CWE Content Team
MITRE
2020-02-24
updated Relationships, Taxonomy_Mappings, Time_of_Introduction

CWE Content Team
MITRE
2020-06-25
updated Relationships

CWE Content Team
MITRE
2020-08-20
updated Alternate_Terms, Relationships

CWE Content Team
MITRE
2020-12-10
updated Alternate_Terms, Observed_Examples, Relationships

CWE Content Team
MITRE
2021-07-20
updated Demonstrative_Examples, Observed_Examples, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2022-06-28
updated Observed_Examples, Relationships

CWE Content Team
MITRE
2022-10-13
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2023-01-31
updated Alternate_Terms, Description

CWE Content Team
MITRE
2023-04-27
updated Potential_Mitigations, References, Relationships, Time_of_Introduction

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes, Relationships

CWE Content Team
MITRE
2024-07-16
4.15
2024-07-16
updated Alternate_Terms, Background_Details, Common_Consequences, Description, Diagram

CWE Content Team
MITRE
2024-11-19
4.16
2024-11-19
updated Description, Relationships

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

CWE Content Team
MITRE
2025-09-09
4.18
2025-09-09
updated Demonstrative_Examples, Detection_Factors, Functional_Areas, References

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

Abhi Balakrishnan
2024-02-29
4.15
2024-07-16
Provided diagram to improve CWE usability

Buffer Errors
Failure to Constrain Operations within the Bounds of an Allocated Memory Buffer
Failure to Constrain Operations within the Bounds of a Memory Buffer