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.)
CWE-126 Variante Borrador
Buffer Over-read
This vulnerability occurs when a program reads data from a memory buffer using an index or pointer that points beyond the buffer's allocated boundary, accessing unintended memory locations.
Definición
What is CWE-126?
This vulnerability occurs when a program reads data from a memory buffer using an index or pointer that points beyond the buffer's allocated boundary, accessing unintended memory locations.
Buffer over-reads happen when software fails to properly validate that a read operation stays within the bounds of a buffer. This can lead to the exposure of sensitive information stored in adjacent memory, cause crashes, or create unexpected program behavior. It's a common pitfall when using low-level languages like C/C++ with functions that don't inherently check boundaries, or when manual bounds checking logic contains errors.
Detecting these flaws manually across a large codebase is challenging. While SAST tools can identify the risky patterns, Plexicus uses AI to not only find them but also generate specific, context-aware fixes—transforming a security finding into a ready-to-apply code suggestion. This automates the remediation step, helping developers secure their applications faster and more consistently.
Impacto en el mundo real
Real-world CVEs caused by CWE-126
-
Text editor has out-of-bounds read past end of line while indenting C code
-
Chain: "Heartbleed" bug receives an inconsistent length parameter (CWE-130) enabling an out-of-bounds read (CWE-126), returning memory that could include private cryptographic keys and other sensitive data.
-
Chain: product does not handle when an input string is not NULL terminated, leading to buffer over-read or heap-based buffer overflow.
Cómo lo explotan los atacantes
Ruta del atacante paso a paso
- 1
In the following C/C++ example the method processMessageFromSocket() will get a message from a socket, placed into a buffer, and will parse the contents of the buffer into a structure that contains the message length and the message body. A for loop is used to copy the message body into a local character string which will be passed to another method for processing.
- 2
However, the message length variable (msgLength) from the structure is used as the condition for ending the for loop without validating that msgLength accurately reflects the actual length of the message body (CWE-606). If msgLength indicates a length that is longer than the size of a message body (CWE-130), then this can result in a buffer over-read by reading past the end of the buffer (CWE-126).
- 3
The following C/C++ example demonstrates a buffer over-read due to a missing NULL terminator. The main method of a pattern matching utility that looks for a specific pattern within a specific file uses the string strncopy() method to copy the command line user input file name and pattern to the Filename and Pattern character arrays respectively.
- 4
However, the code do not take into account that strncpy() will not add a NULL terminator when the source buffer is equal in length of longer than that provide size attribute. Therefore if a user enters a filename or pattern that are the same size as (or larger than) their respective character arrays, a NULL terminator will not be added (CWE-170) which leads to the printf() read beyond the expected end of the Filename and Pattern buffers.
- 5
To fix this problem, be sure to subtract 1 from the sizeof() call to allow room for the null byte to be added.
Ejemplo de código vulnerable
Vulnerable C
In the following C/C++ example the method processMessageFromSocket() will get a message from a socket, placed into a buffer, and will parse the contents of the buffer into a structure that contains the message length and the message body. A for loop is used to copy the message body into a local character string which will be passed to another method for processing.
int processMessageFromSocket(int socket) {
int success;
char buffer[BUFFER_SIZE];
char message[MESSAGE_SIZE];
```
// get message from socket and store into buffer*
*//Ignoring possibliity that buffer > BUFFER_SIZE*
if (getMessage(socket, buffer, BUFFER_SIZE) > 0) {
```
```
// place contents of the buffer into message structure*
ExMessage *msg = recastBuffer(buffer);
*// copy message body into string for processing*
int index;
for (index = 0; index < msg->msgLength; index++) {
```
message[index] = msg->msgBody[index];
}
message[index] = '\0';
```
// process message*
success = processMessage(message);}
return success;} Ejemplo de código seguro
Secure C
To fix this problem, be sure to subtract 1 from the sizeof() call to allow room for the null byte to be added.
```
/* copy filename parameter to variable, no off-by-one overflow */*
strncpy(Filename, argv[2], sizeof(Filename)-1);
Filename[255]='\0';
*/* copy pattern parameter to variable, no off-by-one overflow */*
strncpy(Pattern, argv[3], sizeof(Pattern)-1);Pattern[31]='\0'; What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Lista de prevención
How to prevent CWE-126
- Architecture Use safe-by-default frameworks and APIs that prevent the unsafe pattern from being expressible.
- Implementation Validate input at trust boundaries; use allowlists, not denylists.
- Implementation Apply the principle of least privilege to credentials, file paths, and runtime permissions.
- Testing Cover this weakness in CI: SAST rules + targeted unit tests for the data flow.
- Operation Monitor logs for the runtime signals listed in the next section.
Señales de detección
How to detect CWE-126
Plexicus detecta automáticamente CWE-126 y abre un PR de corrección en menos de 60 segundos.
Codex Remedium escanea cada commit, identifica esta debilidad concreta y entrega un pull request listo para revisión con el parche. Sin tickets. Sin traspasos.
Preguntas frecuentes ¿Qué es CWE-126?
¿Qué gravedad tiene CWE-126?
¿Qué lenguajes o plataformas se ven afectados por CWE-126?
¿Cómo puedo prevenir CWE-126?
¿Cómo detecta y corrige Plexicus CWE-126?
¿Dónde puedo aprender más sobre CWE-126?
Frequently asked questions
¿Qué es CWE-126?
This vulnerability occurs when a program reads data from a memory buffer using an index or pointer that points beyond the buffer's allocated boundary, accessing unintended memory locations.
¿Qué gravedad tiene CWE-126?
MITRE no ha publicado una calificación de probabilidad de explotación para esta debilidad. Trátala como de impacto medio hasta que tu modelo de amenazas demuestre lo contrario.
¿Qué lenguajes o plataformas se ven afectados por CWE-126?
MITRE lists the following affected platforms: C, C++.
¿Cómo puedo prevenir CWE-126?
Use safe-by-default frameworks, validate untrusted input at trust boundaries, and apply the principle of least privilege. Cover the data-flow signature in CI with SAST.
¿Cómo detecta y corrige Plexicus CWE-126?
El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-126 en cada commit. Cuando hay coincidencia, nuestro agente Codex Remedium abre un PR de corrección con el código corregido, las pruebas y un resumen de una línea para el revisor.
¿Dónde puedo aprender más sobre CWE-126?
MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/126.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.
Debilidades relacionadas
Weaknesses related to CWE-126
CWE-788 Padre
Access of Memory Location After End of Buffer
This vulnerability occurs when software attempts to read from or write to a memory buffer using an index or pointer that points past the…
CWE-121 Hermano
Stack-based Buffer Overflow
A stack-based buffer overflow occurs when a program writes more data to a buffer located on the call stack than it can hold, corrupting…
CWE-122 Hermano
Heap-based Buffer Overflow
A heap-based buffer overflow occurs when a program writes more data to a memory buffer allocated in the heap than it can hold, corrupting…
Recursos
Further reading
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