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CWE-203: Information Exposure Through Discrepancy

 
Information Exposure Through Discrepancy
Weakness ID: 203 (Weakness Class)Status: Incomplete
+ Description

Description Summary

The product behaves differently or sends different responses in a way that exposes security-relevant information about the state of the product, such as whether a particular operation was successful or not.
+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms

Languages

All

+ Common Consequences
ScopeEffect
Confidentiality
Access Control

Technical Impact: Read application data; Bypass protection mechanism

An attacker can gain access to sensitive information about the system, including authentication information that may allow an attacker to gain access to the system.

+ Demonstrative Examples

Example 1

The following code checks validity of the supplied username and password and notifies the user of a successful or failed login.

(Bad Code)
Example Language: Perl 
my $username=param('username');
my $password=param('password');

if (IsValidUsername($username) == 1)
{
if (IsValidPassword($username, $password) == 1)
{
print "Login Successful";
}
else
{
print "Login Failed - incorrect password";
}
}
else
{
print "Login Failed - unknown username";
}

In the above code, there are different messages for when an incorrect username is supplied, versus when the username is correct but the password is wrong. This difference enables a potential attacker to understand the state of the login function, and could allow an attacker to discover a valid username by trying different values until the incorrect password message is returned. In essence, this makes it easier for an attacker to obtain half of the necessary authentication credentials.

While this type of information may be helpful to a user, it is also useful to a potential attacker. In the above example, the message for both failed cases should be the same, such as:

(Result)
 
"Login Failed - incorrect username or password"
+ Observed Examples
ReferenceDescription
This, and others, use ".." attacks and monitor error responses, so there is overlap with directory traversal.
Enumeration of valid usernames based on inconsistent responses
Account number enumeration via inconsistent responses.
User enumeration via discrepancies in error messages.
User enumeration via discrepancies in error messages.
Bulletin Board displays different error messages when a user exists or not, which makes it easier for remote attackers to identify valid users and conduct a brute force password guessing attack.
Operating System, when direct remote login is disabled, displays a different message if the password is correct, which allows remote attackers to guess the password via brute force methods.
Product allows remote attackers to determine if a port is being filtered because the response packet TTL is different than the default TTL.
Product sets a different TTL when a port is being filtered than when it is not being filtered, which allows remote attackers to identify filtered ports by comparing TTLs.
Product may generate different responses than specified by the administrator, possibly leading to an information leak.
Version control system allows remote attackers to determine the existence of arbitrary files and directories via the -X command for an alternate history file, which causes different error messages to be returned.
FTP server generates an error message if the user name does not exist instead of prompting for a password, which allows remote attackers to determine valid usernames.
SSL implementation does not perform a MAC computation if an incorrect block cipher padding is used, which causes an information leak (timing discrepancy) that may make it easier to launch cryptographic attacks that rely on distinguishing between padding and MAC verification errors, possibly leading to extraction of the original plaintext, aka the "Vaudenay timing attack."
Virtual machine allows malicious web site operators to determine the existence of files on the client by measuring delays in the execution of the getSystemResource method.
Product uses a shorter timeout for a non-existent user than a valid user, which makes it easier for remote attackers to guess usernames and conduct brute force password guessing.
Product immediately sends an error message when a user does not exist, which allows remote attackers to determine valid usernames via a timing attack.
FTP server responds in a different amount of time when a given username exists, which allows remote attackers to identify valid usernames by timing the server response.
Browser allows remote attackers to determine the existence of arbitrary files by setting the src property to the target filename and using Javascript to determine if the web page immediately stops loading, which indicates whether the file exists or not.
+ Potential Mitigations

Phase: Architecture and Design

Strategy: Separation of Privilege

Compartmentalize the system to have "safe" areas where trust boundaries can be unambiguously drawn. Do not allow sensitive data to go outside of the trust boundary and always be careful when interfacing with a compartment outside of the safe area.

Ensure that appropriate compartmentalization is built into the system design and that the compartmentalization serves to allow for and further reinforce privilege separation functionality. Architects and designers should rely on the principle of least privilege to decide when it is appropriate to use and to drop system privileges.

Phase: Implementation

Ensure that error messages only contain minimal details that are useful to the intended audience, and nobody else. The messages need to strike the balance between being too cryptic and not being cryptic enough. They should not necessarily reveal the methods that were used to determine the error. Such detailed information can be used to refine the original attack to increase the chances of success.

If errors must be tracked in some detail, capture them in log messages - but consider what could occur if the log messages can be viewed by attackers. Avoid recording highly sensitive information such as passwords in any form. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a username is valid or not.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class200Information Exposure
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfCategoryCategory717OWASP Top Ten 2007 Category A6 - Information Leakage and Improper Error Handling
Weaknesses in OWASP Top Ten (2007) (primary)629
ChildOfCategoryCategory728OWASP Top Ten 2004 Category A7 - Improper Error Handling
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory967SFP Secondary Cluster: State Disclosure
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness BaseWeakness Base204Response Discrepancy Information Exposure
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base205Information Exposure Through Behavioral Discrepancy
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base208Information Exposure Through Timing Discrepancy
Development Concepts (primary)699
Research Concepts (primary)1000
MemberOfViewView884CWE Cross-section
CWE Cross-section (primary)884
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERDiscrepancy Information Leaks
OWASP Top Ten 2007A6CWE More SpecificInformation Leakage and Improper Error Handling
OWASP Top Ten 2004A7CWE More SpecificImproper Error Handling
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
PLOVERExternally Mined
Modifications
Modification DateModifierOrganizationSource
2008-07-01Eric DalciCigitalExternal
updated Potential_Mitigations, Time_of_Introduction
2008-09-08CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2009-12-28CWE Content TeamMITREInternal
updated Description, Name
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2012-05-11CWE Content TeamMITREInternal
updated Common_Consequences, Demonstrative_Examples, Observed_Examples, Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2014-07-30CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2009-12-28Discrepancy Information Leaks
Page Last Updated: July 30, 2014