Common Weakness Enumeration

A Community-Developed List of Software Weakness Types

CWE/SANS Top 25 Most Dangerous Software Errors
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CWE-804: Guessable CAPTCHA

Weakness ID: 804
Abstraction: Base
Structure: Simple
Status: Incomplete
Presentation Filter:
+ Description
The software uses a CAPTCHA challenge, but the challenge can be guessed or automatically recognized by a non-human actor.
+ Extended Description

An automated attacker could bypass the intended protection of the CAPTCHA challenge and perform actions at a higher frequency than humanly possible, such as launching spam attacks.

There can be several different causes of a guessable CAPTCHA:

  • An audio or visual image that does not have sufficient distortion from the unobfuscated source image.
  • A question is generated that with a format that can be automatically recognized, such as a math question.
  • A question for which the number of possible answers is limited, such as birth years or favorite sports teams.
  • A general-knowledge or trivia question for which the answer can be accessed using a data base, such as country capitals or popular actors.
  • Other data associated with the CAPTCHA may provide hints about its contents, such as an image whose filename contains the word that is used in the CAPTCHA.
+ 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)
ChildOfClassClass287Improper Authentication
ChildOfClassClass330Use of Insufficiently Random Values
ChildOfClassClass863Incorrect Authorization
+ Relevant to the view "Development Concepts" (CWE-699)
ChildOfClassClass287Improper Authentication
ChildOfClassClass330Use of Insufficiently Random Values
ChildOfClassClass863Incorrect Authorization
+ 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.

Architecture and Design
+ 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)


Web Server (Sometimes Prevalent)

+ 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; Other

When authorization, authentication, or another protection mechanism relies on CAPTCHA entities to ensure that only human actors can access certain functionality, then an automated attacker such as a bot may access the restricted functionality by guessing the CAPTCHA.
+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
+ 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.
MemberOfCategoryCategory8082010 Top 25 - Weaknesses On the Cusp
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
WASC21Insufficient Anti-Automation
+ References
[REF-731] Web Application Security Consortium. "Insufficient Anti-automation". <>.
+ Content History
Submission DateSubmitterOrganization
2010-01-15CWE Content TeamMITRE
New entry to handle anti-automation as identified in WASC.
Modification DateModifierOrganization
2010-06-21CWE Content TeamMITRE
updated Common_Consequences
2011-06-01CWE Content TeamMITRE
updated Common_Consequences, Relationships
2017-11-08CWE Content TeamMITRE
updated Applicable_Platforms, Likelihood_of_Exploit

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Page Last Updated: January 18, 2018