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-167: Improper Handling of Additional Special Element

Weakness ID: 167
Abstraction: Base
Status: Draft
Presentation Filter:
+ Description

Description Summary

The software receives input from an upstream component, but it does not handle or incorrectly handles when an additional unexpected special element is missing.
+ Time of Introduction
  • Implementation
+ Applicable Platforms

Languages

All

+ Common Consequences
ScopeEffect
Integrity

Technical Impact: Unexpected state

+ Observed Examples
ReferenceDescription
Extra "<" in front of SCRIPT tag.
Extra "<" in front of SCRIPT tag.
"<script" - probably a cleansing error
+ Potential Mitigations

Developers should anticipate that extra special elements will be injected in the input vectors of their software system. Use an appropriate combination of black lists and whitelists 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 Class159Failure to Sanitize Special Element
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfWeakness ClassWeakness Class703Improper Check or Handling of Exceptional Conditions
Research Concepts1000
ChildOfCategoryCategory722OWASP Top Ten 2004 Category A1 - Unvalidated Input
Weaknesses in OWASP Top Ten (2004) (primary)711
ChildOfCategoryCategory992SFP Secondary Cluster: Faulty Input Transformation
Software Fault Pattern (SFP) Clusters (primary)888
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
PLOVERExtra Special Element
+ 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
2009-03-10CWE Content TeamMITREInternal
updated Relationships
2009-05-27CWE Content TeamMITREInternal
updated Description, Name
2009-07-27CWE Content TeamMITREInternal
updated Potential_Mitigations
2011-03-29CWE Content TeamMITREInternal
updated 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
2014-07-30CWE Content TeamMITREInternal
updated Relationships
2017-05-03CWE Content TeamMITREInternal
updated Potential_Mitigations
Previous Entry Names
Change DatePrevious Entry Name
2008-04-11Extra Special Element
2009-05-27Failure to Handle Additional Special Element

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Page Last Updated: May 05, 2017