Guessable CAPTCHA
Weakness ID: 804 (Weakness Base)Status: Incomplete
+ Description

Description Summary

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.

+ Time of Introduction
  • Architecture and Design
  • Implementation
+ Applicable Platforms



Technology Classes

Web-Server: (Sometimes)

+ Common Consequences

Technical Impact: Bypass security

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.

+ Likelihood of Exploit

Medium to High

+ Weakness Ordinalities
(where the weakness exists independent of other weaknesses)
+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class285Improper Access Control (Authorization)
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfWeakness ClassWeakness Class287Improper Authentication
Development Concepts699
Research Concepts1000
ChildOfWeakness ClassWeakness Class330Use of Insufficiently Random Values
Development Concepts699
Research Concepts1000
ChildOfCategoryCategory8082010 Top 25 - Weaknesses On the Cusp
Weaknesses in the 2010 CWE/SANS Top 25 Most Dangerous Programming Errors (primary)800
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
WASC21Insufficient Anti-Automation
+ References
Web Application Security Consortium. "Insufficient Anti-automation". <>.
+ Content History
Submission DateSubmitterOrganizationSource
2010-01-15MITREInternal CWE Team
New entry to handle anti-automation as identified in WASC.