CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer
Also known as: Buffer Overflow, buffer overrun, memory safety
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.
Last updated
Overview
CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) is a class-level software weakness catalogued by MITRE in the Common Weakness Enumeration (CWE). It describes a recurring type of mistake that can lead to exploitable security vulnerabilities.
Background
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.
Real-world CVEs
1,804 recorded CVEs are caused by CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), including 45 in CISA's KEV (Known Exploited Vulnerabilities) catalog. KEVs are shown first. 452 new CWE-119 CVEs have been recorded so far in 2026 (364 in 2025).
- CVE-2021-22991CISA KEVCritical · CVSS 10.0 · EPSS 99th2021-03-31
- CVE-2010-3765CISA KEVCritical · CVSS 9.8 · EPSS 100th2010-10-27
- CVE-2008-4250CISA KEVCritical · CVSS 9.8 · EPSS 100th2008-10-23
- CVE-2025-31277CISA KEVCritical · CVSS 9.4 · EPSS 71th2025-07-29
- CVE-2017-6744CISA KEVCritical · CVSS 9.4 · EPSS 94th2017-07-17
- CVE-2013-1690CISA KEVCritical · CVSS 9.4 · EPSS 99th2013-06-26
- CVE-2025-31200CISA KEVCritical · CVSS 9.3 · EPSS 97th2025-04-16
- CVE-2023-4966CISA KEV
Unauthenticated sensitive information disclosure
Critical · CVSS 9.3 · EPSS 100th2023-10-10 - CVE-2020-29557CISA KEVCritical · CVSS 9.3 · EPSS 99th2021-01-29
- CVE-2020-0796CISA KEVCritical · CVSS 9.3 · EPSS 100th2020-03-12
- CVE-2018-0151CISA KEVCritical · CVSS 9.3 · EPSS 96th2018-03-28
- CVE-2018-7445CISA KEVCritical · CVSS 9.3 · EPSS 99th2018-03-19
Showing 12 of 1,804 recorded CWE-119 CVEs. Track new ones as they are published and get AI-written analysis and fixes.
Monitor CWE-119 vulnerabilitiesCommon consequences
What can happen when CWE-119 is exploited.
Execute Unauthorized Code or Commands, Modify Memory
Affects: Integrity, Confidentiality, Availability
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.
Read Memory, DoS: Crash, Exit, or Restart, DoS: Resource Consumption (CPU), DoS: Resource Consumption (Memory)
Affects: Availability, Confidentiality
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.
Read Memory
Affects: Confidentiality
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.
How it happens
When it is introduced
Typically introduced during these phases of the software lifecycle.
Applies to
Languages
How to prevent it
Practical mitigations for CWE-119, grouped by where in the lifecycle they apply.
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.
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.
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
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.
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 — 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].
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].
Effectiveness: 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.
Replace unbounded copy functions with analogous functions that support length arguments, such as strcpy with strncpy. Create these if they are not available.
Effectiveness: 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).
How to detect it
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.
Effectiveness: High
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].
Effectiveness: Moderate
Automated Static Analysis - Binary or Bytecode
According to SOAR [REF-1479], the following detection techniques may be useful:
Effectiveness: SOAR Partial
Manual Static Analysis - Binary or Bytecode
According to SOAR [REF-1479], the following detection techniques may be useful:
Effectiveness: SOAR Partial
Dynamic Analysis with Automated Results Interpretation
According to SOAR [REF-1479], the following detection techniques may be useful:
Effectiveness: SOAR Partial
Dynamic Analysis with Manual Results Interpretation
According to SOAR [REF-1479], the following detection techniques may be useful:
Effectiveness: SOAR Partial
Manual Static Analysis - Source Code
According to SOAR [REF-1479], the following detection techniques may be useful:
Effectiveness: SOAR Partial
Automated Static Analysis - Source Code
According to SOAR [REF-1479], the following detection techniques may be useful:
Effectiveness: High
Architecture or Design Review
According to SOAR [REF-1479], the following detection techniques may be useful:
Effectiveness: High
Code examples
Illustrative examples from MITRE showing how the weakness appears in code.
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.
Vulnerable example
void host_lookup(char *user_supplied_addr){This example applies an encoding procedure to an input string and stores it into a buffer.
Vulnerable example
char * copy_input(char *user_supplied_string){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.
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
Vulnerable example
int getValueFromArray(int *array, int len, int index) {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.
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
Illustrative examples
Real CVEs that MITRE cites as examples of this weakness.
- CVE-2021-22991CISA KEV— Incorrect URI normalization in application traffic product leads to buffer overflow, as exploited in the wild per CISA KEV.
- CVE-2020-29557CISA KEV— Buffer overflow in Wi-Fi router web interface, as exploited in the wild per CISA KEV.
- CVE-2025-47153 — Chain: build process for JavaScript runtime environment can have inconsistent sizes for off_t (CWE-1102), allowing out-of-bounds access / segmentation fault (CWE-119)
- CVE-2009-2550 — Classic stack-based buffer overflow in media player using a long entry in a playlist
- CVE-2009-2403 — Heap-based buffer overflow in media player using a long entry in a playlist
- CVE-2009-0689 — large precision value in a format string triggers overflow
- CVE-2009-0690 — negative offset value leads to out-of-bounds read
- CVE-2009-1532 — malformed inputs cause accesses of uninitialized or previously-deleted objects, leading to memory corruption
- CVE-2009-1528 — chain: lack of synchronization leads to memory corruption
- 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)
- CVE-2009-0558 — attacker-controlled array index leads to code execution
- CVE-2009-0269 — chain: -1 value from a function call was intended to indicate an error, but is used as an array index instead.
- CVE-2009-0566 — chain: incorrect calculations lead to incorrect pointer dereference and memory corruption
- CVE-2009-1350 — product accepts crafted messages that lead to a dereference of an arbitrary pointer
- CVE-2009-0191 — chain: malformed input causes dereference of uninitialized memory
- CVE-2008-4113 — OS kernel trusts userland-supplied length value, allowing reading of sensitive information
- 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.
- CVE-2003-0542 — buffer overflow involving a regular expression with a large number of captures
- CVE-2017-1000121 — chain: unchecked message size metadata allows integer overflow (CWE-190) leading to buffer overflow (CWE-119).
Terminology & mappings
Alternate terms
- 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.
Mapped taxonomies
- OWASP Top Ten 2004: Buffer Overflows (A5) — Exact fit
- CERT C Secure Coding: Understand how arrays work (ARR00-C)
- CERT C Secure Coding: Do not form or use out-of-bounds pointers or array subscripts (ARR30-C) — CWE More Abstract fit
- CERT C Secure Coding: Guarantee that library functions do not form invalid pointers (ARR38-C) — CWE More Abstract fit
- CERT C Secure Coding: Do not make assumptions about the size of an environment variable (ENV01-C)
- CERT C Secure Coding: Do not access a variable through a pointer of an incompatible type (EXP39-C) — Imprecise fit
- CERT C Secure Coding: Do not assume character data has been read (FIO37-C)
- CERT C Secure Coding: Guarantee that storage for strings has sufficient space for character data and the null terminator (STR31-C) — CWE More Abstract fit
- CERT C Secure Coding: Do not pass a non-null-terminated character sequence to a library function that expects a string (STR32-C) — CWE More Abstract fit
- WASC: Buffer Overflow (7)
- Software Fault Patterns: Faulty Buffer Access (SFP8)
Attack patterns
CAPEC attack patterns that exploit this weakness.
- CAPEC-10: Buffer Overflow via Environment Variables
- CAPEC-100: Overflow Buffers
- CAPEC-123: Buffer Manipulation
- CAPEC-14: Client-side Injection-induced Buffer Overflow
- CAPEC-24: Filter Failure through Buffer Overflow
- CAPEC-42: MIME Conversion
- CAPEC-44: Overflow Binary Resource File
- CAPEC-45: Buffer Overflow via Symbolic Links
- CAPEC-46: Overflow Variables and Tags
- CAPEC-47: Buffer Overflow via Parameter Expansion
- CAPEC-8: Buffer Overflow in an API Call
- CAPEC-9: Buffer Overflow in Local Command-Line Utilities
Frequently asked questions
Common questions about CWE-119.
- What is CWE-119?
- 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.
- What CVEs are caused by CWE-119?
- 1,804 recorded CVEs are attributed to CWE-119, including CVE-2021-22991, CVE-2010-3765, CVE-2008-4250. 45 are listed in CISA's Known Exploited Vulnerabilities (KEV) catalog.
- Is CWE-119 part of the OWASP Top 10?
- CWE-119 maps to OWASP Top Ten 2004: Buffer Overflows (A5) in the OWASP security taxonomy.
- How do you prevent CWE-119?
- Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- How is CWE-119 detected?
- 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.
- What are the consequences of CWE-119?
- Exploiting CWE-119 can lead to: Execute Unauthorized Code or Commands, Modify Memory, Read Memory, DoS: Crash, Exit, or Restart, DoS: Resource Consumption (CPU), DoS: Resource Consumption (Memory).
- Is CWE-119 actively exploited?
- Yes. 45 CWE-119 vulnerabilities are in CISA's KEV catalog of actively exploited flaws, out of 1,804 recorded CVEs.
References
- MITRE CWE definition (CWE-119) (opens in a new tab)
- CWE-119 vulnerabilities on NVD (opens in a new tab)
- Learn: What is a CWE?
Weakness data is sourced from the MITRE CWE catalog (v4.20). CVE associations are aggregated and kept current by RadicalNotion.AI.
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