Duolingo: A tale of two APIs

Hi, I’m Duo the owl!

The Researcher’s Dilemma

Response from HackerOne

Summary of findings (if you read no further)

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3,000,000 (estimated worldwide Plus users) * $120 (yearly subscription cost) = $360,000,000 in annual revenue lost.

Path to discovery

Path to exploitation

1. Free Perks

2. Duplicate submission of practice routines

3. Duplicate submission of profile updates

Note: the XP field in the payload with value set to 5000 as an example amount
Before: 10,334
After: 15,334
After, after: 50,016,894

Impact

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Jon Roethke

Jon Roethke

information security, blockchain, travel, surf https://waymobetta.com