CWE-804: Guessable CAPTCHA
The product uses a CAPTCHA challenge, but the challenge can be guessed or automatically recognized by a non-human actor.
How it's found
Guessable CAPTCHA is typically found by tracing untrusted input from where it enters the system to the point where it is used without the check or neutralization this weakness describes, combining manual code review with dynamic testing.
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 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 entertainers. 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.
Consequences
- 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.
Where this fits in a TurboPentest engagement
This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.
Frequently asked questions
What is CWE-804?
The product uses a CAPTCHA challenge, but the challenge can be guessed or automatically recognized by a non-human actor.
How do you find Guessable CAPTCHA?
Guessable CAPTCHA is typically found by tracing untrusted input from where it enters the system to the point where it is used without the check or neutralization this weakness describes, combining manual code review with dynamic testing.
What is the impact of CWE-804?
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.
Does TurboPentest test for Guessable CAPTCHA?
This weakness is not covered by the automated black-box pentest. IntegSec pentesters cover it in a manual engagement.
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Written and reviewed by
Michel Chamberland - Founder & CEO, IntegSec
CISSP, OSCP, OSCE, CEH, GIAC, CCSK · 20+ years in offensive security
Michel has spent 20+ years on offensive security teams including IBM X-Force Red and Trustwave SpiderLabs, leading penetration tests, red team engagements, and breach response for Fortune 500 customers. He is the founder of IntegSec and the architect of TurboPentest.
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