CWE

Guessable CAPTCHA

ID: 804		Date: (C)2012-05-14   (M)2022-10-10
Type: weakness		Status: INCOMPLETE
Abstraction Type: Base

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.

Likelihood of Exploit: Medium to High

Applicable Platforms
Language Class: Language-independent
Technology Class: Sometimes
Technology Class: Web-Server

Time Of Introduction

• Architecture and Design
• Implementation

Common Consequences

Scope	Technical Impact	Notes
Access_Control Other	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.

Detection Methods
None

Potential Mitigations
None

Relationships

Related CWE	Type	View	Chain
CWE-804 ChildOf CWE-330	Weakness	CWE-1000 CWE-699

Demonstrative Examples
None

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

Taxynomy	Id	Name	Fit
WASC	21	Insufficient Anti-Automation

References:

1. Web Application Security Consortium .Insufficient Anti-automation.