CWE

Response Discrepancy Information Exposure

ID: 204		Date: (C)2012-05-14   (M)2022-10-10
Type: weakness		Status: INCOMPLETE
Abstraction Type: Base

Description

The software provides different responses to incoming requests in a way that allows an actor to determine system state information that is outside of that actor's control sphere.

Extended Description

This issue frequently occurs during authentication, where a difference in failed-login messages could allow an attacker to determine if the username is valid or not. These exposures can be inadvertent (bug) or intentional (design).

Applicable Platforms
Language Class: All

Time Of Introduction

• Architecture and Design
• Implementation

Common Consequences

Scope	Technical Impact	Notes
Confidentiality Access_Control	Read application data Bypass protection mechanism

Detection Methods
None

Potential Mitigations

Phase	Strategy	Description	Effectiveness	Notes
Architecture and Design	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.
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
can overlap errors related to escalated privileges

Related CWE	Type	View	Chain
CWE-204 ChildOf CWE-895	Category	CWE-888

Demonstrative Examples   (Details)

1. The following code checks validity of the supplied username and password and notifies the user of a successful or failed login. (Demonstrative Example Id DX-38)

Observed Examples

1. CVE-2002-2094 : This, and others, use ".." attacks and monitor error responses, so there is overlap with directory traversal.
2. CVE-2001-1483 : Enumeration of valid usernames based on inconsistent responses
3. CVE-2001-1528 : Account number enumeration via inconsistent responses.
4. CVE-2004-2150 : User enumeration via discrepancies in error messages.
5. CVE-2005-1650 : User enumeration via discrepancies in error messages.
6. CVE-2004-0294 : 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.
7. CVE-2004-0243 : 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.
8. CVE-2002-0514 : Product allows remote attackers to determine if a port is being filtered because the response packet TTL is different than the default TTL.
9. CVE-2002-0515 : 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.
10. CVE-2001-1387 : Product may generate different responses than specified by the administrator, possibly leading to an information leak.
11. CVE-2004-0778 : 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.
12. CVE-2004-1428 : 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.

For more examples, refer to CVE relations in the bottom box.

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

Taxynomy	Id	Name	Fit
PLOVER		Response discrepancy infoleak

References:

1. Michael Howard David LeBlanc John Viega .24 Deadly Sins of Software Security. McGraw-Hill. Section:'"Sin 12: Information Leakage." Page 191'. Published on 2010.