Common Weakness Enumeration

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CWE-178: Improper Handling of Case Sensitivity

Weakness ID: 178
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.
+ Extended Description

Improperly handled case sensitive data can lead to several possible consequences, including:

  • case-insensitive passwords reducing the size of the key space, making brute force attacks easier
  • bypassing filters or access controls using alternate names
  • multiple interpretation errors using alternate names.
+ Relationships

The table(s) below shows the weaknesses and high level categories that are related to this weakness. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore.

+ Relevant to the view "Research Concepts" (CWE-1000)
ChildOfClassClass - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. More general than a Base weakness.706Use of Incorrectly-Resolved Name or Reference
CanPrecedeVariantVariant - a weakness that is described at a very low level of detail, typically limited to a specific language or technology. More specific than a Base weakness.289Authentication Bypass by Alternate Name
CanPrecedeVariantVariant - a weakness that is described at a very low level of detail, typically limited to a specific language or technology. More specific than a Base weakness.433Unparsed Raw Web Content Delivery
+ Relevant to the view "Development Concepts" (CWE-699)
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.171Cleansing, Canonicalization, and Comparison Errors
+ Modes Of Introduction

The different Modes of Introduction provide information about how and when this weakness may be introduced. The Phase identifies a point in the software life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase.

+ Applicable Platforms
The listings below show possible areas for which the given weakness could appear. These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. The platform is listed along with how frequently the given weakness appears for that instance.


Class: Language-Independent (Undetermined Prevalence)

+ Common Consequences

The table below specifies different individual consequences associated with the weakness. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.

Access Control

Technical Impact: Bypass Protection Mechanism

+ Demonstrative Examples

Example 1

In the following example, an XSS neutralization method replaces script tags in user supplied input with a safe equivalent:

(bad code)
Example Language: Java 
public String preventXSS(String input, String mask) {
return input.replaceAll("script", mask);

The code only works when the "script" tag is in all lower-case, forming an incomplete blacklist (CWE-184). Equivalent tags such as "SCRIPT" or "ScRiPt" will not be neutralized by this method, allowing an XSS attack.

+ Observed Examples
Application server allows attackers to bypass execution of a jsp page and read the source code using an upper case JSP extension in the request.
The server is case sensitive, so filetype handlers treat .jsp and .JSP as different extensions. JSP source code may be read because .JSP defaults to the filetype "text".
The server is case sensitive, so filetype handlers treat .jsp and .JSP as different extensions. JSP source code may be read because .JSP defaults to the filetype "text".
A URL that contains some characters whose case is not matched by the server's filters may bypass access restrictions because the case-insensitive file system will then handle the request after it bypasses the case sensitive filter.
Server allows remote attackers to obtain source code of CGI scripts via URLs that contain MS-DOS conventions such as (1) upper case letters or (2) 8.3 file names.
Task Manager does not allow local users to end processes with uppercase letters named (1) winlogon.exe, (2) csrss.exe, (3) smss.exe and (4) services.exe via the Process tab which could allow local users to install Trojan horses that cannot be stopped.
chain: Code was ported from a case-sensitive Unix platform to a case-insensitive Windows platform where filetype handlers treat .jsp and .JSP as different extensions. JSP source code may be read because .JSP defaults to the filetype "text".
Leads to interpretation error
Directories may be listed because lower case web requests are not properly handled by the server.
File extension check in forum software only verifies extensions that contain all lowercase letters, which allows remote attackers to upload arbitrary files via file extensions that include uppercase letters.
Web server restricts access to files in a case sensitive manner, but the filesystem accesses files in a case insensitive manner, which allows remote attackers to read privileged files using alternate capitalization.
Case insensitive passwords lead to search space reduction.
HTTP server allows bypass of access restrictions using URIs with mixed case.
Mixed upper/lowercase allows bypass of ACLs.
Bypass malicious script detection by using tokens that aren't case sensitive.
Mixed case problem allows "admin" to have "Admin" rights (alternate name property).
Chain: uppercase file extensions causes web server to return script source code instead of executing the script.
+ Potential Mitigations

Phase: Architecture and Design

Strategy: Input Validation

Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.

Phase: Implementation

Strategy: Input Validation

Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a whitelist of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.

When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."

Do not rely exclusively on looking for malicious or malformed inputs (i.e., do not rely on a blacklist). A blacklist is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, blacklists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.

Phase: Implementation

Strategy: Input Validation

Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass whitelist validation schemes by introducing dangerous inputs after they have been checked.
+ Functional Areas
  • File Processing
+ Affected Resources
  • File or Directory
+ Memberships
This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. This information is often useful in understanding where a weakness fits within the context of external information sources.
MemberOfCategoryCategory - a CWE entry that contains a set of other entries that share a common characteristic.992SFP Secondary Cluster: Faulty Input Transformation
+ Notes

Research Gap

These are probably under-studied in Windows and Mac environments, where file names are case-insensitive and thus are subject to equivalence manipulations involving case.
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERCase Sensitivity (lowercase, uppercase, mixed case)
+ Content History
Submission DateSubmitterOrganization
Modification DateModifierOrganization
2008-07-01Sean EidemillerCigital
added/updated demonstrative examples
2008-07-01Eric DalciCigital
updated Potential_Mitigations, Time_of_Introduction
2008-09-08CWE Content TeamMITRE
updated Description, Relationships, Observed_Example, Taxonomy_Mappings
2008-10-14CWE Content TeamMITRE
updated Observed_Examples
2008-11-24CWE Content TeamMITRE
updated Observed_Examples
2009-03-10CWE Content TeamMITRE
updated Description
2009-07-27CWE Content TeamMITRE
updated Potential_Mitigations
2010-06-21CWE Content TeamMITRE
updated Demonstrative_Examples
2010-12-13CWE Content TeamMITRE
updated Name
2011-03-29CWE Content TeamMITRE
updated Potential_Mitigations
2011-06-01CWE Content TeamMITRE
updated Common_Consequences
2012-05-11CWE Content TeamMITRE
updated Observed_Examples, Relationships
2012-10-30CWE Content TeamMITRE
updated Demonstrative_Examples, Potential_Mitigations
2014-07-30CWE Content TeamMITRE
updated Relationships
2017-11-08CWE Content TeamMITRE
updated Affected_Resources, Applicable_Platforms, Functional_Areas, Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Case Sensitivity (Lowercase, Uppercase, Mixed Case)
2010-12-13Failure to Resolve Case Sensitivity

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Page Last Updated: December 27, 2018