Addition of Data Structure Sentinel
Weakness ID: 464 (Weakness Base)Status: Incomplete
+ Description

Description Summary

The accidental addition of a data-structure sentinel can cause serious programming logic problems.

Extended Description

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.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

C

C++

+ Common Consequences
ScopeEffect
Availability

Generally this error will cause the data structure to not work properly by truncating the data.

+ Likelihood of Exploit

High to Very High

+ Demonstrative Examples

Example 1

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.

(Bad Code)
Example Languages: C and C++ 
char *foo;
foo=malloc(sizeof(char)*5);
foo[0]='a';
foo[1]='a';
foo[2]=atoi(getc(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);

The first print statement will print each character separated by a space. However, if a non-integer is read from stdin by getc, then atoi will not make a conversion and return 0. When foo is printed as a string, the 0 at character foo[2] will act as a NULL terminator and foo[3] will never be printed.

+ Potential Mitigations

Phases: Implementation; Architecture and Design

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

Phase: 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.

Phase: Requirements

Use a language or compiler that performs automatic bounds checking.

Phase: Architecture and Design

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

Phase: Build and Compilation

Compiler-based canary mechanisms such as StackGuard, ProPolice, and Microsoft Visual Studio /GS flag. Unless this provides automatic bounds checking, it is not a complete solution.

Phase: Operation

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

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class138Improper Sanitization of Special Elements
Research Concepts (primary)1000
ChildOfCategoryCategory461Data Structure Issues
Development Concepts (primary)699
ChildOfCategoryCategory741CERT C Secure Coding Section 07 - Characters and Strings (STR)
Weaknesses Addressed by the CERT C Secure Coding Standard (primary)734
PeerOfWeakness BaseWeakness Base170Improper Null Termination
Research Concepts1000
PeerOfWeakness BaseWeakness Base463Deletion of Data Structure Sentinel
Research Concepts1000
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CLASPAddition of data-structure sentinel
CERT C Secure CodingSTR03-CDo not inadvertently truncate a null-terminated byte string
CERT C Secure CodingSTR06-CDo not assume that strtok() leaves the parse string unchanged
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
CLASPExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Time of Introduction
2008-09-08CWE Content TeamMITREInternal
updated Applicable Platforms, Common Consequences, Relationships, Other Notes, Taxonomy Mappings
2008-11-24CWE Content TeamMITREInternal
updated Relationships, Taxonomy Mappings
2009-07-27CWE Content TeamMITREInternal
updated Demonstrative Examples, Description, Other Notes, Potential Mitigations, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Addition of Data-structure Sentinel
Back to top