Run static analysis (SAST) on the codebase looking for the unsafe pattern in the data flow.
CWE-1285 Base Incomplete
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…
Definition
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.
Real-world impact
Real-world CVEs caused by CWE-1285
-
large ID in packet used as array index
-
negative array index as argument to POP LIST command
How attackers exploit it
Step-by-step attacker path
- 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.
Vulnerable code example
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;
}
...
} Secure code example
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.
Prevention checklist
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.
Detection signals
How to detect CWE-1285
Run dynamic application security testing against the live endpoint.
Watch runtime logs for unusual exception traces, malformed input, or authorization bypass attempts.
Code review: flag any new code that handles input from this surface without using the validated framework helpers.
Plexicus auto-detects CWE-1285 and opens a fix PR in under 60 seconds.
Codex Remedium scans every commit, identifies this exact weakness, and ships a reviewer-ready pull request with the patch. No tickets. No hand-offs.
Frequently asked questions What is CWE-1285?
How serious is CWE-1285?
What languages or platforms are affected by CWE-1285?
How can I prevent CWE-1285?
How does Plexicus detect and fix CWE-1285?
Where can I learn more about CWE-1285?
Frequently asked questions
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.
How serious is CWE-1285?
MITRE has not published a likelihood-of-exploit rating for this weakness. Treat it as medium-impact until your threat model proves otherwise.
What languages or platforms are affected by CWE-1285?
MITRE has not specified affected platforms for this CWE — it can apply across most application stacks.
How can I prevent 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…
How does Plexicus detect and fix CWE-1285?
Plexicus's SAST engine matches the data-flow signature for CWE-1285 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.
Where can I learn more about CWE-1285?
MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/1285.html. You can also reference OWASP and NIST documentation for adjacent guidance.
Related weaknesses
Weaknesses related to CWE-1285
CWE-20 Parent
Improper Input Validation
This vulnerability occurs when an application accepts data from an external source but fails to properly verify that the data is safe and…
CWE-102 Sibling
Struts: Duplicate Validation Forms
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CWE-103 Sibling
Struts: Incomplete validate() Method Definition
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CWE-104 Sibling
Struts: Form Bean Does Not Extend Validation Class
This vulnerability occurs in Apache Struts applications when a form bean class does not properly extend the framework's validation class.…
CWE-105 Sibling
Struts: Form Field Without Validator
This vulnerability occurs when a Struts application form contains an input field that lacks a corresponding validator, leaving it open to…
CWE-106 Sibling
Struts: Plug-in Framework not in Use
This weakness occurs when a Java application, particularly one using the Struts framework, does not implement a structured input…
CWE-107 Sibling
Struts: Unused Validation Form
This vulnerability occurs when a Struts application contains validation form definitions that are no longer linked to any active form or…
CWE-108 Sibling
Struts: Unvalidated Action Form
In Apache Struts, every Action Form that processes user input must have a corresponding validation form configured. Missing this…
CWE-109 Sibling
Struts: Validator Turned Off
This vulnerability occurs when an application built with Apache Struts intentionally disables its built-in validation framework. By…
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