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Hacking and defeating Google's reCAPTCHA with a 99% accuracy
"Note: In the hours before our presentation/release, Google pushed a new version of reCAPTCHA which fully nerfs our attack."
- drharris 14y agoAfter so much work, gotta love the footnote here: "Note: In the hours before our presentation/release, Google pushed a new version of reCAPTCHA which fully nerfs our attack."
- bmj1 14y agoYes - I almost missed that - that should be highlighted more clearly not buried in a footnote - as it undermines the impact of the research...
- eli 14y agoThe research is just as solid as it ever was, it just minimizes the immediate, real-world effects.
- Karunamon 14y agoI'd be willing to wager that Google has many different versions of ReCaptcha sitting on ice, to be shifted into production if a flaw in the current system is found. I've noticed some different image captchas floating around too.
- barik 14y agoThis isn't a huge problem for security people. Indeed, at most academic security conferences, by the time you present your work it has usually already been broken and/or countered. To goal of good research (and one that differentiates researchers from criminals) is to present a proof of concept and to advance the state of security. The fact that security is a perpetual arms race is incidental. Well, at least that's what security researchers tell themselves anyway to avoid going mad. :)
- JackC 14y agoWhat makes it funny is that the bulk of the article isn't "here's how we did it and what we learned," but "here's what you need to do to get our code running on Ubuntu." Then you get to the footnote: "PS: It's pointless to get our code running on Ubuntu." I spent the whole article wondering why they were so interested not only in presenting a proof of concept, but in getting as many people as possible actively breaking captchas. Then I got to the end and switched to wondering whether the whole thing is an elaborate prank.
- barik 14y agoYes, I thought this particular link was perhaps not the best way to present the work, mainly because the interesting part is actually this: "We accomplished this with a combination of Machine Learning, hashing methods, keyspace reduction tactics, and taking advantage of an overall limited number of captchas. Specifically, Stiltwalker goes head to head against reCAPTCHA'S audio captcha system and defeats all but a sliver of it's challenges." On the other hand, it looks like they provide a corpus (http://www.dc949.org/projects/stiltwalker/stiltwalker-corpus.tar http://www.dc949.org/projects/stiltwalker/stiltwalker-corpus...) [1.5 GB!] that you can still use to run the program.
- djKianoosh 14y agoStill, the important takeaway for webapp developers is never to rely on just one form of protection. Add timestamp checks, honeypots, etc, in addition to captcha and use them appropriately for your application.
- drone 14y agoAlas, I'm running a handful of websites, and nearly nothing works, outside of stopping the most egregious of automated bots. Every new protection technique seems to be broken fairly fast. The best results so far have been combining basic WAF techniques (like placing poisoned form fields re-named as regular form fields and randomizing the names of standard form fields, one-time hash values in required fields, etc.) with some form of captcha. However, every day five or six make it through. Observing their patterns and timing, and the fact that they make zero mistakes while interacting very slowly with the site, I can only presume that humans are directly involved as well, either as mechanical turks or simply manually posting the spam. notably, they follow normal, guided flows through the site - not like robots at all, but hit pages that would obviously be interesting to a human (say, have a certain type of image content linking them versus another), while avoiding the least popular pages - never hit urls that are hidden via CSS, etc.
- seanp2k2 14y agoYup; human spammers are awful. Labor is so cheap now that it's financially viable to pay people to spam sites in some cases. The Internet is a sad place indeed.
- dutchbrit 14y agoI actually tried hacking reCaptha via audio and the Google Speech to text API a few days ago. It didn't work unfortunately, it really frustrates me at times when I have to refresh reCaptcha 10 times to actually be able to read the damn thing!!
- robotmay 14y agoWhat problems did you run into when trying to use the speech API? It's quite an interesting avenue for bypassing these in the future as speech recognition gets better. Also highly entertaining when you use Google's own service against them.
- dutchbrit 14y agoExactly my thought, with using their own service! The thing was, is that the background noise made the API not recognise the actual words (I think - since you can't really "debug"), but maybe if you reduce the noise, it might be possible - I wanted to give that a go, but haven't had a chance yet. I just don't know of any ways to automatically reduce noise.
- deleted 14y ago[deleted]
- coldpie 14y agoI suspect you haven't gotten around to it, but did you study the noise at all? According to Wikipedia <http://en.wikipedia.org/wiki/Voice_frequency> http://en.wikipedia.org/wiki/Voice_frequency>, 85-255 Hz is the usual range of human speech. You could try a band-pass filter with that pass band, and probably a pretty high roll-off (this will cut off sounds like S and X, but I suspect voice recognition software is often capable of dealing with those, given how often they fail to be represented well in discrete audio). Audacity can do this, and there's almost certainly automatible tools out there. Worth a shot, anyway.
- dutchbrit 14y ago
- monsterix 14y agoNow here is some serious hacker's news! Was getting nagged by 'what NewEgg can/can't do' posts off late.
- omonra 14y agoThis may be very interesting to crack, but who is responsible for Google making their CAPTCHA almost impossible for human to decipher now? I seriously have to click 5 times before even seeing anything resembling letters I can parse
- duiker101 14y agoI didn't go in depth of the article/method but from what I've read it takes advantages of the audio function not the images.
- verroq 14y agoYou only have the type one word correct, and they make sure one word is readable so with some practice you can easily recognise which word is the key-word.
- ohgodthecat3 14y agoHe isn't speaking of reCAPTCHA but google's nearly impossible to read captchas that take way too much time to decipher. If you'd like to see it you can usually get it by putting in a bad password to a gmail account too many times (though I don't know if that has other consequences). Edit: Here is an image example http://www.techian.com/wp-content/uploads/captcha.png http://www.techian.com/wp-content/uploads/captcha.png
- simonbrown 14y agoStrange they don't use reCAPTCHA for this.
- verroq 14y agoOh those, yeah they are very hard to decipher.
- sp332 14y agoI wonder what they do for non-Latin locales?
- 14y ago
- s_henry_paulson 14y agoHere's the Ars Technica article which does much better job explaining the system: http://arstechnica.com/security/2012/05/google-recaptcha-brought-to-its-knees/ http://arstechnica.com/security/2012/05/google-recaptcha-bro...
- ahmadss 14y agoagreed, thanks for posting the ars link. the youtube video in the OP does a great job of explaining and the thinking behind the attack, and even though it's an hour long, it's worth the watch.
- seanp2k2 14y agoVideo tutorials are awful if they're the only option. I read very quickly, and videos are typically paced at the lowest "average" comprehension level, so they're a painfully inefficient way to relay technical information. Plain text wins again, at least for one-way technical communication.
- eli 14y agoI tend to agree with you, but FYI you sound pretty arrogant when you say it that way.
- dunmalg 14y agoHow about when I say I hate videos of what should be written text because years of exposure to gunfire in the Army has impaired my hearing? I will never understand why people think that the crappy audio channel of a youtube video of some guy "umming" and gulping through a poorly prepared speech, all recorded on a $5 microphone, is a suitable way of passing information.
- danso 14y agoIn systems that are less secured than Google, the audio catchpa seems trivial to break...I think I've seen one on court sites that read a combination of numbers from 1 to 9 with some variance in the vocal speed. I'm not an audio engineer but that seems fairly trivial to crack (though maybe their visual catchpa would be easier...I dunno, not an expert in OCR either). It's a good lesson in a form of social engineering. Sites have to provide this alternative access for the visually impaired...yet I bet the resources/creativity put behind it is not at the same level as the kind put into the catchpa used by 99% of the userbase. Furthermore, the most important client -- your boss -- is likely to not be blind him/herself, which eliminates that extra critical layer of oversight.
- throwaway1979 14y agoGoogle's captcha system is horrid. I've mentioned this to people on the accessibility team but to no avail. They used to have a wheel chair icon next to the bloody scrambled text. I taught a computer class to seniors and it was painful watching them deal with the account sign up process (also, I thought it was insulting asking a mobile senior to click on the wheel chair icon ... to the designer ... FU!). Clicking on the wheel chair would give audio that barely made any sense to me. The whole process was stupid. Like many others, I can barely get through their captcha service. I'm actually happy people circumvented it. Maybe someone will think it through this time around.
- tmh88j 14y agoI also thought that was insulting with the wheel chair icon. A person in a wheel chair has problems walking, not (necessarily) their vision. How about "Help" in text?...less confusion and possible anger
- excuse-me 14y agoSince the point of the audio version is not to be hit with lawsuits under the ADA - perhaps it should just be a little icon of a lawyer?
- deleted 14y ago[deleted]
- PassTheAmmo 14y agoI imaging that whole sites could be designed using only your proposed lawyer icon, possibly with some additional icon representing political correctness.
- Graphon 14y agoWhat's the international symbol for a lawyer? https://www.google.com/search?q=parasite+icon https://www.google.com/search?q=parasite+icon
- ceejayoz 14y ago
- roguecoder 14y agoPretty sure I don't have 99% accuracy at solving reCAPTCHAs. Perhaps it's become a CAPITCHA, Completely Automated Public Inverse Turing test to tell Computers and Humans Apart...
- apendleton 14y agoOne exciting thing about this: the entire model of reCaptcha (at least the text ones; I assume the audio ones are similar) is to make people do useful work when solving captchas by having them complete tasks that they consider too hard for computers to do well (in the text reCaptcha case, OCR). If someone writes software that can defeat the captcha, it does mean the security model is broken, but it also means the state of OCR technology (or audio recognition or whatever) has been advanced, and the digitization of books that had previously required human intervention can now be accomplished by automated means. In other words, spammers are incidentally creating the tools to expand the scope of digital human knowledge. Win-win, really.
- vhf 14y agohttp://xkcd.com/810/ http://xkcd.com/810/ Win-win, really. :)
- aptwebapps 14y agoAre the audio versions sourced from recordings that need transcription as the visual versions are sourced from scanned documents? I assumed that was just to improve access. If not, then it isn't useful work, really.
- vhf 14y agoLooking at how the hacked it, we can safely deduce the audio version is only to improve access. Useless for transcription, because it 'validates' phonetically. This is part of the attack : Whether audio is "wagon" or "van", the 'word' "wagn" validates. Same for "Spoon" and "Teaspoon", which both can be validate by entering "Tspoon". (Since Ts can be said "Ss" as in "Tsunami" (Sunami) and "T S" as in T-Rex.)
- apendleton 14y agoThat's a shame. I would imagine that a productively similar audio task could be devised around humans helping to transcribe hard-to-auto-transcribe audio recordings, and that it could use a similar strategy to the visual one: a known-good clip and an ambiguous one, requiring the user to transcribe both.
- verroq 14y agoTheir testing and high success rates on the public Google reCaptcha test probably tipped off a Google employee internally.
- zackattack 14y agoOr you could just look at the $ value of your time and realize it's cheaper to just buy CAPTCHAs. There are services that provide labor to unemployed persons in lesser developed countries. Excuse the flamebait, I just want to alert y'all to the possibility.
- Graphon 14y ago> Note: In the hours before our presentation/release, Google pushed a new version of reCAPTCHA which fully nerfs our attack. I take it that "fully nerfs" means this defeat of recaptcha is no longer useful?
- kedyr2 14y agocaptchas are very annoying. it is surprising that they have lasted this long. what would be the best alternatives?
- TillE 14y agoObscurity. If you're not a significant target, you can get by with simpler methods. Deciphering obfuscated text is one of very few verifiable tasks that humans can do which computers cannot. Alternatively, you can look at other methods of identity verification. If you ask for $5 to create an account, you'll have few spam problems.
- joelthelion 14y agoWhat are we going to do once all CAPTCHAS are completely broken?
- neotek 14y agoCAPTCHAs are ultimately already completely broken - they don't really slow anyone down except ordinary users, because spammers are using human labour to solve CAPTCHAs at the rate of one or two dollars per thousand solved.
- wendsday 14y agoA company that relies on a bot that accesses others' resources to make money and at the same time relies on reCAPTCHA to frustrate other bots from accessing it own resources. It may be easy to do today, but, going forward, how do we determine which bots are "good" and which ones are "bad"? Clearly, simply being a "bot" does not imply "bad" intent. If it did then we should all be blocking search engine bots. Yet this is what reCAPTCHA does: it blocks not based on intent, but based on the characteristic of being a "bot".
- akincisor 14y agoIt's easy. One bot reads a text file and only accesses the resources outlined in the file. The other maliciously tries to eat up resources without restraint. Good - Bad.
- wendsday 14y agoLike I said, it's relatively easy today. But how about going forward? There will be lots more bots and lots more usages. Things might not be so simple. For example, some sites might exclude all search engine bots except a chosen few despite the fact they all honor robots.txt and behave essentially the same. (BTW, if by "text file" you mean robots.txt, isn't that an exclusion list? You seem to be saying it's an inclusion list.)
- cheatercheater 14y agoHere's a local company that promises to change that: http://www.captchaad.com/ http://www.captchaad.com/ I think they may become successful for the time being, although they have some issues with UX and technology they need to work out first. What they do is they display a short ad video and have the user answer a comprehension question. Apparently it's not as hackable, although I'm not sure how that will work if they become popular: Producing a video is fairly difficult, so you can only have so many videos running, and I can entirely see a cracking group able to simply watch every possible video and crack it. Recognizing videos from a finite set of possibilities is a solved problem. However, as long as they're not huuuuge, they're better than reCaptcha. I think currently everything that is popular will be cracked sooner or later, so the only hope is in people having new ideas. This becomes less of an art now and more of an unending race. So for the time being, Captcha Ad seem to be OK. The ads they place are acceptable, and they pay loads more than the typical ad box, which is good. They're only doing germany right now, but they have plans entering the english-speaking market.