Difference between revisions of "Often Misused: String Management"

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==Abstract==
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[[ASDR_TOC_Vulnerabilities|Vulnerabilities Table of Contents]]
  
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==Description==
 
Functions that convert between Multibyte and Unicode strings encourage buffer overflows.
 
Functions that convert between Multibyte and Unicode strings encourage buffer overflows.
 
==Description==
 
  
 
Windows provides the MultiByteToWideChar(), WideCharToMultiByte(), UnicodeToBytes, and BytesToUnicode functions to convert between arbitrary multibyte (usually ANSI) character strings and Unicode (wide character) strings. The size arguments to these functions are specified in different units – one in bytes, the other in characters – making their use prone to error. In a multibyte character string, each character occupies a varying number of bytes, and therefore the size of such strings is most easily specified as a total number of bytes. In Unicode, however, characters are always a fixed size, and string lengths are typically given by the number of characters they contain. Mistakenly specifying the wrong units in a size argument can lead to a buffer overflow.
 
Windows provides the MultiByteToWideChar(), WideCharToMultiByte(), UnicodeToBytes, and BytesToUnicode functions to convert between arbitrary multibyte (usually ANSI) character strings and Unicode (wide character) strings. The size arguments to these functions are specified in different units – one in bytes, the other in characters – making their use prone to error. In a multibyte character string, each character occupies a varying number of bytes, and therefore the size of such strings is most easily specified as a total number of bytes. In Unicode, however, characters are always a fixed size, and string lengths are typically given by the number of characters they contain. Mistakenly specifying the wrong units in a size argument can lead to a buffer overflow.
  
==Examples ==
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==Risk Factors==
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TBD
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==Examples==
  
 
The following function takes a username specified as a multibyte string and a pointer to a structure for user information and populates the structure with information about the specified user. Since Windows authentication uses Unicode for usernames, the username argument is first converted from a multibyte string to a Unicode string.
 
The following function takes a username specified as a multibyte string and a pointer to a structure for user information and populates the structure with information about the specified user. Since Windows authentication uses Unicode for usernames, the username argument is first converted from a multibyte string to a Unicode string.
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This function incorrectly passes the size of unicodeUser in bytes instead of characters. The call to MultiByteToWideChar() can therefore write up to (UNLEN+1)*sizeof(WCHAR) wide characters, or (UNLEN+1)*sizeof(WCHAR)* sizeof(WCHAR) bytes, to the unicodeUser array, which has only (UNLEN+1)*sizeof(WCHAR) bytes allocated. If the username string contains more than UNLEN characters, the call to MultiByteToWideChar() will overflow the buffer unicodeUser.
 
This function incorrectly passes the size of unicodeUser in bytes instead of characters. The call to MultiByteToWideChar() can therefore write up to (UNLEN+1)*sizeof(WCHAR) wide characters, or (UNLEN+1)*sizeof(WCHAR)* sizeof(WCHAR) bytes, to the unicodeUser array, which has only (UNLEN+1)*sizeof(WCHAR) bytes allocated. If the username string contains more than UNLEN characters, the call to MultiByteToWideChar() will overflow the buffer unicodeUser.
  
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==Related [[Attacks]]==
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* [[Attack 1]]
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* [[Attack 2]]
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==Related [[Vulnerabilities]]==
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* [[Buffer Overflow]]
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==Related [[Controls]]==
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* [[Control 1]]
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* [[Control 2]]
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==Related [[Technical Impacts]]==
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* [[Technical Impact 1]]
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* [[Technical Impact 2]]
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==References==
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TBD
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[[Category:FIXME|add links
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In addition, one should classify vulnerability based on the following subcategories: Ex:<nowiki>[[Category:Error Handling Vulnerability]]</nowiki>
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Availability Vulnerability
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Authorization Vulnerability
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Authentication Vulnerability
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Concurrency Vulnerability
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Configuration Vulnerability
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Cryptographic Vulnerability
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Encoding Vulnerability
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Error Handling Vulnerability
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Input Validation Vulnerability
  
==Related Threats==
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Logging and Auditing Vulnerability
  
==Related Attacks==
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Session Management Vulnerability]]
  
==Related Vulnerabilities==
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__NOTOC__
  
==Related Countermeasures==
 
  
==Categories==
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[[Category:OWASP ASDR Project]]
 
[[Category:Use of Dangerous API]]
 
[[Category:Use of Dangerous API]]
 
[[Category:Implementation]]
 
[[Category:Implementation]]
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[[Category:Code Snippet]]
 
[[Category:Code Snippet]]
 
[[Category:Windows]]
 
[[Category:Windows]]
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[[Category:API Abuse]]
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[[Category:Vulnerability]]

Latest revision as of 20:50, 20 February 2009

This is a Vulnerability. To view all vulnerabilities, please see the Vulnerability Category page.


This article includes content generously donated to OWASP by Fortify.JPG.

Last revision (mm/dd/yy): 02/20/2009

Vulnerabilities Table of Contents

Description

Functions that convert between Multibyte and Unicode strings encourage buffer overflows.

Windows provides the MultiByteToWideChar(), WideCharToMultiByte(), UnicodeToBytes, and BytesToUnicode functions to convert between arbitrary multibyte (usually ANSI) character strings and Unicode (wide character) strings. The size arguments to these functions are specified in different units – one in bytes, the other in characters – making their use prone to error. In a multibyte character string, each character occupies a varying number of bytes, and therefore the size of such strings is most easily specified as a total number of bytes. In Unicode, however, characters are always a fixed size, and string lengths are typically given by the number of characters they contain. Mistakenly specifying the wrong units in a size argument can lead to a buffer overflow.


Risk Factors

TBD


Examples

The following function takes a username specified as a multibyte string and a pointer to a structure for user information and populates the structure with information about the specified user. Since Windows authentication uses Unicode for usernames, the username argument is first converted from a multibyte string to a Unicode string.

	void getUserInfo(char *username, struct _USER_INFO_2 info){
		WCHAR unicodeUser[UNLEN+1];
		MultiByteToWideChar(CP_ACP, 0, username, -1,
				  unicodeUser, sizeof(unicodeUser));
		NetUserGetInfo(NULL, unicodeUser, 2, (LPBYTE *)&info);
	}

This function incorrectly passes the size of unicodeUser in bytes instead of characters. The call to MultiByteToWideChar() can therefore write up to (UNLEN+1)*sizeof(WCHAR) wide characters, or (UNLEN+1)*sizeof(WCHAR)* sizeof(WCHAR) bytes, to the unicodeUser array, which has only (UNLEN+1)*sizeof(WCHAR) bytes allocated. If the username string contains more than UNLEN characters, the call to MultiByteToWideChar() will overflow the buffer unicodeUser.

Related Attacks


Related Vulnerabilities

Related Controls


Related Technical Impacts


References

TBD