The product writes data past the end, or before the beginning, of the intended buffer.

Resultant
At the point when the product writes data to an invalid location, it is likely that a separate weakness already occurred earlier. For example, the product might alter an index, perform incorrect pointer arithmetic, initialize or release memory incorrectly, etc., thus referencing a memory location outside the buffer.

Memory Corruption
Often used to describe the consequences of writing to memory outside the bounds of a buffer, or to memory that is otherwise invalid.

Implementation

High

Integrity
Modify Memory
Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.

Availability
DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.

Other
Unexpected State
Subsequent write operations can produce undefined or unexpected results.

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.

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).

The following code attempts to save four different identification numbers into an array.

int id_sequence[3];
/* Populate the id array. */
id_sequence[0] = 123;id_sequence[1] = 234;id_sequence[2] = 345;id_sequence[3] = 456;

Since the array is only allocated to hold three elements, the valid indices are 0 to 2; so, the assignment to id_sequence[3] is out of bounds.

In the following code, it is possible to request that memcpy move a much larger segment of memory than assumed:

int returnChunkSize(void *) {

/* if chunk info is valid, return the size of usable memory,

* else, return -1 to indicate an error

*/
...
}int main() {...memcpy(destBuf, srcBuf, (returnChunkSize(destBuf)-1));...}

If returnChunkSize() happens to encounter an error it will return -1. Notice that the return value is not checked before the memcpy operation (CWE-252), so -1 can be passed as the size argument to memcpy() (CWE-805). Because memcpy() assumes that the value is unsigned, it will be interpreted as MAXINT-1 (CWE-195), and therefore will copy far more memory than is likely available to the destination buffer (CWE-787, CWE-788).

This code takes an IP address from the user and verifies that it is well formed. It 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 code 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.

In the following C/C++ code, a utility function is used to trim trailing whitespace from a character string. The function copies the input string to a local character string and uses a while statement to remove the trailing whitespace by moving backward through the string and overwriting whitespace with a NUL character.

char* trimTrailingWhitespace(char *strMessage, int length) {
char *retMessage;char *message = malloc(sizeof(char)*(length+1));

// copy input string to a temporary string
char message[length+1];int index;for (index = 0; index < length; index++) {message[index] = strMessage[index];}message[index] = '\0';

// trim trailing whitespace
int len = index-1;while (isspace(message[len])) {message[len] = '\0';len--;}

// return string without trailing whitespace
retMessage = message;return retMessage;
}

However, this function can cause a buffer underwrite if the input character string contains all whitespace. On some systems the while statement will move backwards past the beginning of a character string and will call the isspace() function on an address outside of the bounds of the local buffer.

The following code allocates memory for a maximum number of widgets. It then gets a user-specified number of widgets, making sure that the user does not request too many. It then initializes the elements of the array using InitializeWidget(). Because the number of widgets can vary for each request, the code inserts a NULL pointer to signify the location of the last widget.

int i;unsigned int numWidgets;Widget **WidgetList;
numWidgets = GetUntrustedSizeValue();if ((numWidgets == 0) || (numWidgets > MAX_NUM_WIDGETS)) {ExitError("Incorrect number of widgets requested!");}WidgetList = (Widget **)malloc(numWidgets * sizeof(Widget *));printf("WidgetList ptr=%p\n", WidgetList);for(i=0; i<numWidgets; i++) {WidgetList[i] = InitializeWidget();}WidgetList[numWidgets] = NULL;showWidgets(WidgetList);

However, this code contains an off-by-one calculation error (CWE-193). It allocates exactly enough space to contain the specified number of widgets, but it does not include the space for the NULL pointer. As a result, the allocated buffer is smaller than it is supposed to be (CWE-131). So if the user ever requests MAX_NUM_WIDGETS, there is an out-of-bounds write (CWE-787) when the NULL is assigned. Depending on the environment and compilation settings, this could cause memory corruption.

The following is an example of code that may result in a buffer underwrite. This code is attempting to replace the substring "Replace Me" in destBuf with the string stored in srcBuf. It does so by using the function strstr(), which returns a pointer to the found substring in destBuf. Using pointer arithmetic, the starting index of the substring is found.

int main() {
...
char *result = strstr(destBuf, "Replace Me");
int idx = result - destBuf;
strcpy(&destBuf[idx], srcBuf);
...}

In the case where the substring is not found in destBuf, strstr() will return NULL, causing the pointer arithmetic to be undefined, potentially setting the value of idx to a negative number. If idx is negative, this will result in a buffer underwrite of destBuf.

CVE-2025-27363
Font rendering library does not properly
handle assigning a signed short value to an unsigned
long (CWE-195), leading to an integer wraparound
(CWE-190), causing too small of a buffer (CWE-131),
leading to an out-of-bounds write
(CWE-787).
https://www.cve.org/CVERecord?id=CVE-2025-27363

CVE-2023-1017
The reference implementation code for a Trusted Platform Module does not implement length checks on data, allowing for an attacker to write 2 bytes past the end of a buffer.
https://www.cve.org/CVERecord?id=CVE-2023-1017

CVE-2021-21220
Chain: insufficient input validation (CWE-20) in browser allows heap corruption (CWE-787), as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2021-21220

CVE-2021-28664
GPU kernel driver allows memory corruption because a user can obtain read/write access to read-only pages, as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2021-28664

CVE-2020-17087
Chain: integer truncation (CWE-197) causes small buffer allocation (CWE-131) leading to out-of-bounds write (CWE-787) in kernel pool, as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2020-17087

CVE-2020-1054
Out-of-bounds write in kernel-mode driver, as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2020-1054

CVE-2020-0041
Escape from browser sandbox using out-of-bounds write due to incorrect bounds check, as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2020-0041

CVE-2020-0968
Memory corruption in web browser scripting engine, as exploited in the wild per CISA KEV.
https://www.cve.org/CVERecord?id=CVE-2020-0968

CVE-2020-0022
chain: mobile phone Bluetooth implementation does not include offset when calculating packet length (CWE-682), leading to out-of-bounds write (CWE-787)
https://www.cve.org/CVERecord?id=CVE-2020-0022

CVE-2019-1010006
Chain: compiler optimization (CWE-733) removes or modifies code used to detect integer overflow (CWE-190), allowing out-of-bounds write (CWE-787).
https://www.cve.org/CVERecord?id=CVE-2019-1010006

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-2009-0269
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-2002-2227
Unchecked length of SSLv2 challenge value leads to buffer underflow.
https://www.cve.org/CVERecord?id=CVE-2002-2227

CVE-2007-4580
Buffer underflow from a small size value with a large buffer (length parameter inconsistency, CWE-130)
https://www.cve.org/CVERecord?id=CVE-2007-4580

CVE-2007-4268
Chain: integer signedness error (CWE-195) passes signed comparison, leading to heap overflow (CWE-122)
https://www.cve.org/CVERecord?id=CVE-2007-4268

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

Memory Management

Memory

Part 3-3
Req SR 3.5

Part 4-1
Req SI-1

Part 4-1
Req SI-2

Part 4-1
Req SVV-1

Part 4-1
Req SVV-3

Part 4-2
Req CR 3.5

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.

CWE Content Team
MITRE
2009-10-21
1.6
2009-10-29

CWE Content Team
MITRE
2010-02-16
updated Demonstrative_Examples

CWE Content Team
MITRE
2010-09-27
updated Relationships

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2014-06-23
updated Demonstrative_Examples

CWE Content Team
MITRE
2015-12-07
updated Relationships

CWE Content Team
MITRE
2018-03-27
updated Description

CWE Content Team
MITRE
2019-09-19
updated Applicable_Platforms, Demonstrative_Examples, Detection_Factors, Likelihood_of_Exploit, Observed_Examples, Potential_Mitigations, References, Relationships, Time_of_Introduction

CWE Content Team
MITRE
2020-02-24
updated Observed_Examples, Relationships

CWE Content Team
MITRE
2020-06-25
updated Observed_Examples

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

CWE Content Team
MITRE
2020-12-10
updated Relationships

CWE Content Team
MITRE
2021-03-15
updated Demonstrative_Examples

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

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

CWE Content Team
MITRE
2022-10-13
updated Applicable_Platforms

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

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

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

CWE Content Team
MITRE
2024-02-29
4.14
2024-02-29
updated Demonstrative_Examples

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

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

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

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

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

"Mapping CWE to 62443" Sub-Working Group
CWE-CAPEC ICS/OT SIG
2023-04-25
Suggested mappings to ISA/IEC 62443.

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