One-letter URL encoding bypass exposed Hugging Face chat admin API, bulk export of private chats
cyb3rops · x · 2026-11-06
Security researcher v12sec disclosed an admin API bypass in Hugging Face's chat: changing the letter a in POST /admin/export to its URL-encoded form (/%61dmin/export) turned a 401 Unauthorized response into a 202 Accepted.
- The bypass allowed a single unauthenticated request to trigger bulk internal exports of every user's private chats.
- The root cause is a routing/normalization inconsistency in how the admin path is validated.
- Full exploitation walkthrough shared in a thread; a textbook case of parser differential leading to privilege bypass.
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