BaseIncompleteCWE-170

CWE-170: Improper Null Termination

Description

The product does not terminate or incorrectly terminates a string or array with a null character or equivalent terminator.

Null termination errors frequently occur in two different ways. An off-by-one error could cause a null to be written out of bounds, leading to an overflow. Or, a program could use a strncpy() function call incorrectly, which prevents a null terminator from being added at all. Other scenarios are possible.

Abstraction: BaseA weakness specific enough to point to detection and prevention methods.
Likelihood of exploit: Medium
Status: Incomplete

Common consequences

ConfidentialityIntegrityAvailability
Read Memory; Execute Unauthorized Code or Commands
The case of an omitted null character is the most dangerous of the possible issues. This will almost certainly result in information disclosure, and possibly a buffer overflow condition, which may be exploited to execute arbitrary code.
ConfidentialityIntegrityAvailability
DoS: Crash, Exit, or Restart; Read Memory; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
If a null character is omitted from a string, then most string-copying functions will read data until they locate a null character, even outside of the intended boundaries of the string. This could: cause a crash due to a segmentation fault cause sensitive adjacent memory to be copied and sent to an outsider trigger a...
IntegrityAvailability
Modify Memory; DoS: Crash, Exit, or Restart
Misplaced null characters may result in any number of security problems. The biggest issue is a subset of buffer overflow, and write-what-where conditions, where data corruption occurs from the writing of a null character over valid data, or even instructions. A randomly placed null character may put the system into an...
IntegrityConfidentialityAvailabilityAccess ControlOther
Alter Execution Logic; Execute Unauthorized Code or Commands
Should the null character corrupt the process flow, or affect a flag controlling access, it may lead to logical errors which allow for the execution of arbitrary code.

Potential mitigations

Requirements
Use a language that is not susceptible to these issues. However, be careful of null byte interaction errors (CWE-626) with lower-level constructs that may be written in a language that is susceptible.
Implementation
Ensure that all string functions used are understood fully as to how they append null characters. Also, be wary of off-by-one errors when appending nulls to the end of strings.
Implementation
If performance constraints permit, special code can be added that validates null-termination of string buffers, this is a rather naive and error-prone solution.
Implementation
Switch to bounded string manipulation functions. Inspect buffer lengths involved in the buffer overrun trace reported with the defect.
Implementation
Add code that fills buffers with nulls (however, the length of buffers still needs to be inspected, to ensure that the non null-terminated string is not written at the physical end of the buffer).

Related weaknesses

Parent weaknesses

CWE-707Improper Neutralization

Can lead to

Peers

Can also be

CWE-147Improper Neutralization of Input Terminators

CAPEC attack patterns that exploit it

CWE 4.20 links no CAPEC attack pattern to this weakness.

Description

The product does not terminate or incorrectly terminates a string or array with a null character or equivalent terminator.

Common consequences

ConfidentialityIntegrityAvailability

Read Memory; Execute Unauthorized Code or Commands

The case of an omitted null character is the most dangerous of the possible issues. This will almost certainly result in information disclosure, and possibly a buffer overflow condition, which may be exploited to execute arbitrary code.

ConfidentialityIntegrityAvailability

DoS: Crash, Exit, or Restart; Read Memory; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)

If a null character is omitted from a string, then most string-copying functions will read data until they locate a null character, even outside of the intended boundaries of the string. This could: cause a crash due to a segmentation fault cause sensitive adjacent memory to be copied and sent to an outsider trigger a...

IntegrityAvailability

Modify Memory; DoS: Crash, Exit, or Restart

Misplaced null characters may result in any number of security problems. The biggest issue is a subset of buffer overflow, and write-what-where conditions, where data corruption occurs from the writing of a null character over valid data, or even instructions. A randomly placed null character may put the system into an...

IntegrityConfidentialityAvailabilityAccess ControlOther

Alter Execution Logic; Execute Unauthorized Code or Commands

Should the null character corrupt the process flow, or affect a flag controlling access, it may lead to logical errors which allow for the execution of arbitrary code.

Potential mitigations

Requirements

Use a language that is not susceptible to these issues. However, be careful of null byte interaction errors (CWE-626) with lower-level constructs that may be written in a language that is susceptible.

Implementation

Ensure that all string functions used are understood fully as to how they append null characters. Also, be wary of off-by-one errors when appending nulls to the end of strings.

Implementation

If performance constraints permit, special code can be added that validates null-termination of string buffers, this is a rather naive and error-prone solution.

Implementation

Switch to bounded string manipulation functions. Inspect buffer lengths involved in the buffer overrun trace reported with the defect.

Implementation

Add code that fills buffers with nulls (however, the length of buffers still needs to be inspected, to ensure that the non null-terminated string is not written at the physical end of the buffer).