CWE

Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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ID

CWE-159: Failure to Sanitize Special Element

Weakness ID: 159
Abstraction: Class
Status: Draft
Presentation Filter:
+ Description

Description Summary

Weaknesses in this attack-focused category do not properly filter and interpret special elements in user-controlled input which could cause adverse effect on the software behavior and integrity.
+ Terminology Notes

Precise terminology for the underlying weaknesses does not exist. Therefore, these weaknesses use the terminology associated with the manipulation.

+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

All

+ Common Consequences
ScopeEffect
Integrity

Technical Impact: Unexpected state

+ Potential Mitigations

Developers should anticipate that special elements will be injected/removed/manipulated in the input vectors of their software system. Use an appropriate combination of black lists and white lists to ensure only valid, expected and appropriate input is processed by the system.

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: Output Encoding

While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict whitelist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).

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.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class138Improper Neutralization of Special Elements
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfCategoryCategory990SFP Secondary Cluster: Tainted Input to Command
Software Fault Pattern (SFP) Clusters (primary)888
ParentOfWeakness VariantWeakness Variant160Improper Neutralization of Leading Special Elements
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant162Improper Neutralization of Trailing Special Elements
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness VariantWeakness Variant164Improper Neutralization of Internal Special Elements
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base166Improper Handling of Missing Special Element
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base167Improper Handling of Additional Special Element
Development Concepts (primary)699
Research Concepts (primary)1000
ParentOfWeakness BaseWeakness Base168Improper Handling of Inconsistent Special Elements
Development Concepts (primary)699
Research Concepts (primary)1000
+ Research Gaps

Customized languages and grammars, even those that are specific to a particular product, are potential sources of weaknesses that are related to special elements. However, most researchers concentrate on the most commonly used representations for data transmission, such as HTML and SQL. Any representation that is commonly used is likely to be a rich source of weaknesses; researchers are encouraged to investigate previously unexplored representations.

+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERCommon Special Element Manipulations
Software Fault PatternsSFP24Tainted input to command
+ Maintenance Notes

The list of children for this entry is far from complete.

+ 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, Other_Notes, Taxonomy_Mappings
2009-07-27CWE Content TeamMITREInternal
updated Potential_Mitigations
2009-10-29CWE Content TeamMITREInternal
updated Maintenance_Notes, Other_Notes, Terminology_Notes
2011-03-29CWE Content TeamMITREInternal
updated Description, Potential_Mitigations
2011-06-01CWE Content TeamMITREInternal
updated Common_Consequences
2011-06-27CWE Content TeamMITREInternal
updated Common_Consequences
2012-05-11CWE Content TeamMITREInternal
updated Relationships
2012-10-30CWE Content TeamMITREInternal
updated Potential_Mitigations
2014-06-23CWE Content TeamMITREInternal
updated Other_Notes
2014-07-30CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Common Special Element Manipulations

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Page Last Updated: January 18, 2017