How to "defeat" Google Audio Recapcha?

Overview of unCapcha - small tool to "pass thru" audio capcha 
26 October 2017   2229

Across the Internet, hundreds of thousands of sites rely on Google's reCaptcha system for defense against bots (in fact, Devpost uses reCaptcha when creating a new account). After a Google research team demonstrated a near complete defeat of the text reCaptcha in 2012, the reCaptcha system evolved to rely on audio and image challenges, historically more difficult challenges for automated systems to solve. Google has continually iterated on its design, releasing a newer and more powerful version as recently as just this year. Successfully demonstrating a defeat of this captcha system spells significant vulnerability for hundreds of thousands of popular sites.

What is unCapcha?

UnCaptcha system has attack capabilities written for the audio captcha. Using browser automation software, we can interact with the target website and engage with the captcha, parsing out the necessary elements to begin the attack. We rely primarily on the audio captcha attack - by properly identifying spoken numbers, we can pass the reCaptcha programmatically and fool the site into thinking our bot is a human. Specifically, unCaptcha targets the popular site Reddit by going through the motions of creating a new user, although unCaptcha stops before creating the user to mitigate the impact on Reddit.


Google's reCaptcha system uses an advanced risk analysis system to determine programmatically how likely a given user is to be a human or a bot. It takes into account your cookies (and by extension, your interaction with other Google services), the speed at which challenges are solved, mouse movements, and (obviously) how successfully you solve the given task. As the system gets increasingly suspicious, it delivers increasingly difficult challenges, and requires the user to solve more of them. Researchers have already identified minor weaknesses with the reCaptcha system - 9 days of legitimate (ish) interaction with Google's services is usually enough to lower the system's suspicion level significantly.

How it works

The format of the audio captcha is a varied-length series of numbers spaced out read aloud at varied speeds, pitches, and accents through background noise. To attack this captcha, the audio payload is identified on the page, downloaded, and automatically split by locations of speech.

From there, each number audio bit is uploaded to 6 different free, online audio transcription services (IBM, Google Cloud, Google Speech Recognition, Sphinx, Wit-AI, Bing Speech Recognition), and these results are collected. Developers ensemble the results from each of these to probabilistically enumerate the most likely string of numbers with a predetermined heuristic. These numbers are then organically typed into the captcha, and the captcha is completed. From testing, team has seen 92%+ accuracy in individual number identification, and 85%+ accuracy in defeating the audio captcha in its entirety.

Python News Digest 5 - 11.10

Learn how to create a Python C extension module, write DNS server in Python, why floating point numbers lie and other interesting things
11 October 2019   96

Greetings! I hope your week went great! Here's new Frontend news digest.

Learn about hash tables, adding maps to django webapp with and about fast HTTP clients. Also, long podcast will give you the tips on how to "win" interview on Python tech vacancy.


        • Hash tables

        Learn about hash tables are, why they are being used them, and how they’re used to implement dictionaries in the most popular Python interpreter: CPython.

        • Building a Python C Extension Module

        Tutorial that will show you how to create Python interfaces in C and other things.

        • How to Add Maps to Django Web App Projects with Mapbox

        Instruction on how to add maps and location-based data to your web applications using Mapbox.

        • Write your own DNS server in Python hosted on Kubernetes

        Tutorial with code example on the topic, mentioned in the header

        • Python and fast HTTP clients

        Big guide on HTTP clients in Python


        • PyPy’s New JSON Parser

        Article covers the decisions that were made to develop the new and improved parser.

        • Six Django template tags not often used in tutorials

        Covers "unpopular" template tags for Django

        • The Numbers, They Lie

        They really do? 

        • Is Rectified Adam (RAdam) Actually Better Than Adam (optimizer)?

        *spoiler* According to author's 24 experiemnts - no.


        • Winning the Python software interview

        James Timmins from RealPython talks what to do at software interview.