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CWE-1285 Base Incompleto
Improper Validation of Specified Index, Position, or Offset in Input
This vulnerability occurs when software accepts user input to determine a location—like an array index, file position, or memory offset—but fails to properly check if that location is safe and valid…
Definición
What is CWE-1285?
This vulnerability occurs when software accepts user input to determine a location—like an array index, file position, or memory offset—but fails to properly check if that location is safe and valid before using it.
Many software resources, like arrays in memory or files on disk, are accessed using numerical positions. When an application trusts user-supplied numbers for these positions without rigorous checks, attackers can supply crafted values that point outside the intended boundaries. This can lead directly to severe consequences like reading or corrupting adjacent memory (buffer overflows), forcing the allocation of huge amounts of resources, or causing the application to crash.
To prevent this, developers must treat all input that defines a position as untrusted. Always validate that the specified index or offset falls within the exact, current bounds of the target resource before any access is performed. Implementing strict range checking is a critical first line of defense to ensure the software only interacts with authorized sections of data.
Impacto en el mundo real
Real-world CVEs caused by CWE-1285
-
large ID in packet used as array index
-
negative array index as argument to POP LIST command
Cómo lo explotan los atacantes
Ruta del atacante paso a paso
- 1
The following example retrieves the sizes of messages for a pop3 mail server. The message sizes are retrieved from a socket that returns in a buffer the message number and the message size, the message number (num) and size (size) are extracted from the buffer and the message size is placed into an array using the message number for the array index.
- 2
In this example the message number retrieved from the buffer could be a value that is outside the allowable range of indices for the array and could possibly be a negative number. Without proper validation of the value to be used for the array index an array overflow could occur and could potentially lead to unauthorized access to memory addresses and system crashes. The value of the array index should be validated to ensure that it is within the allowable range of indices for the array as in the following code.
- 3
In the following example the method displayProductSummary is called from a Web service servlet to retrieve product summary information for display to the user. The servlet obtains the integer value of the product number from the user and passes it to the displayProductSummary method. The displayProductSummary method passes the integer value of the product number to the getProductSummary method which obtains the product summary from the array object containing the project summaries using the integer value of the product number as the array index.
- 4
In this example the integer value used as the array index that is provided by the user may be outside the allowable range of indices for the array which may provide unexpected results or cause the application to fail. The integer value used for the array index should be validated to ensure that it is within the allowable range of indices for the array as in the following code.
- 5
An alternative in Java would be to use one of the collection objects such as ArrayList that will automatically generate an exception if an attempt is made to access an array index that is out of bounds.
Ejemplo de código vulnerable
Vulnerable C
The following example retrieves the sizes of messages for a pop3 mail server. The message sizes are retrieved from a socket that returns in a buffer the message number and the message size, the message number (num) and size (size) are extracted from the buffer and the message size is placed into an array using the message number for the array index.
```
/* capture the sizes of all messages */*
int getsizes(int sock, int count, int *sizes) {
```
...
char buf[BUFFER_SIZE];
int ok;
int num, size;
```
// read values from socket and added to sizes array*
while ((ok = gen_recv(sock, buf, sizeof(buf))) == 0)
{
```
```
// continue read from socket until buf only contains '.'*
if (DOTLINE(buf))
```
break;
else if (sscanf(buf, "%d %d", &num, &size) == 2)
sizes[num - 1] = size;
}
...
} Ejemplo de código seguro
Secure C
In this example the message number retrieved from the buffer could be a value that is outside the allowable range of indices for the array and could possibly be a negative number. Without proper validation of the value to be used for the array index an array overflow could occur and could potentially lead to unauthorized access to memory addresses and system crashes. The value of the array index should be validated to ensure that it is within the allowable range of indices for the array as in the following code.
```
/* capture the sizes of all messages */*
int getsizes(int sock, int count, int *sizes) {
```
...
char buf[BUFFER_SIZE];
int ok;
int num, size;
```
// read values from socket and added to sizes array*
while ((ok = gen_recv(sock, buf, sizeof(buf))) == 0)
{
```
```
// continue read from socket until buf only contains '.'*
if (DOTLINE(buf))
```
break;
else if (sscanf(buf, "%d %d", &num, &size) == 2) {
if (num > 0 && num <= (unsigned)count)
sizes[num - 1] = size;
else
```
/* warn about possible attempt to induce buffer overflow */*
report(stderr, "Warning: ignoring bogus data for message sizes returned by server.\n");}}
```
...
} 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-1285
- Implementation Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Señales de detección
How to detect CWE-1285
Ejecuta pruebas dinámicas de seguridad de aplicaciones (DAST) contra el endpoint en vivo.
Vigila los logs en tiempo de ejecución para detectar trazas de excepción inusuales, entradas malformadas o intentos de bypass de autorización.
Revisión de código: marca cualquier código nuevo que maneje entrada desde esta superficie sin usar los helpers validados del framework.
Plexicus detecta automáticamente CWE-1285 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-1285?
¿Qué gravedad tiene CWE-1285?
¿Qué lenguajes o plataformas se ven afectados por CWE-1285?
¿Cómo puedo prevenir CWE-1285?
¿Cómo detecta y corrige Plexicus CWE-1285?
¿Dónde puedo aprender más sobre CWE-1285?
Frequently asked questions
¿Qué es CWE-1285?
This vulnerability occurs when software accepts user input to determine a location—like an array index, file position, or memory offset—but fails to properly check if that location is safe and valid before using it.
¿Qué gravedad tiene CWE-1285?
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-1285?
MITRE no ha especificado plataformas afectadas para esta CWE — puede aplicar a la mayoría de los stacks de aplicaciones.
¿Cómo puedo prevenir CWE-1285?
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and…
¿Cómo detecta y corrige Plexicus CWE-1285?
El motor SAST de Plexicus detecta la firma de flujo de datos para CWE-1285 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-1285?
MITRE publica la definición canónica en https://cwe.mitre.org/data/definitions/1285.html. También puedes consultar la documentación de OWASP y NIST para guías relacionadas.
Debilidades relacionadas
Weaknesses related to CWE-1285
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