The accidental addition of a data-structure sentinel can cause serious programming logic problems.
Data-structure sentinels are often used to mark the structure of data. A common example of this is the null character at the end of strings or a special sentinel to mark the end of a linked list. It is dangerous to allow this type of control data to be easily accessible. Therefore, it is important to protect from the addition or modification of sentinels.

Primary

Resultant

Implementation

High

Integrity
Modify Application Data
Generally this error will cause the data structure to not work properly by truncating the data.

Implementation
Architecture and Design
Encapsulate the user from interacting with data sentinels. Validate user input to verify that sentinels are not present.

Implementation
Proper error checking can reduce the risk of inadvertently introducing sentinel values into data. For example, if a parsing function fails or encounters an error, it might return a value that is the same as the sentinel.

Architecture and Design
Use an abstraction library to abstract away risky APIs. This is not a complete solution.

Operation
Use OS-level preventative functionality. This is not a complete solution.

The following example assigns some
character values to a list of characters and prints
them each individually, and then as a string. The third
character value is intended to be an integer taken from
user input and converted to an int. The first print
statement will print each character separated by a
space.

char *foo;
foo=malloc(sizeof(char)*5);
foo[0]='a';
foo[1]='a';
foo[2]=fgetc(stdin);
foo[3]='c';
foo[4]='\0';
printf("%c %c %c %c %c \n",foo[0],foo[1],foo[2],foo[3],foo[4]);
printf("%s\n",foo);

However, if a NULL byte is read from stdin
by fgetc, then it will return 0. When foo is printed as
a string, the 0 at character foo[2] will act as a NULL
terminator, and the second printf() statement will
not print foo[3].

Addition of data-structure sentinel

STR03-C
Do not inadvertently truncate a null-terminated byte string

STR06-C
Do not assume that strtok() leaves the parse string unchanged

Allowed
This CWE entry is at the Base level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

CLASP
2006-07-19
Draft 3
2006-07-19

Eric Dalci
Cigital
2008-07-01
updated Time_of_Introduction

CWE Content Team
MITRE
2008-09-08
updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings

CWE Content Team
MITRE
2008-11-24
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2009-07-27
updated Demonstrative_Examples, Description, Other_Notes, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2011-06-01
updated Common_Consequences

CWE Content Team
MITRE
2011-06-27
updated Common_Consequences

CWE Content Team
MITRE
2011-09-13
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-05-11
updated Relationships

CWE Content Team
MITRE
2012-10-30
updated Potential_Mitigations

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Demonstrative_Examples, Likelihood_of_Exploit, Taxonomy_Mappings

CWE Content Team
MITRE
2020-02-24
updated References, Relationships

CWE Content Team
MITRE
2023-04-27
updated Relationships, Time_of_Introduction

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-04-03
4.17
2025-04-03
updated Demonstrative_Examples

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Demonstrative_Examples, Weakness_Ordinalities

Jason Xu
2024-07-20
4.17
2025-04-03
Reported compilation error with demonstrative example.

Addition of Data-structure Sentinel