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OpenAdvisories
Critical · 9.1 CVE-2026-33640 EUVD-2026-16415

Outline has a rate limit bypass that allows brute force of email login OTP

Published Mar 26, 2026 · Updated Apr 1, 2026 · Assigned by GitHub_M

Description

Outline is a service that allows for collaborative documentation. Outline implements an Email OTP login flow for users not associated with an Identity Provider. Starting in version 0.86.0 and prior to version 1.6.0, Outline does not invalidate OTP codes based on amount or frequency of invalid submissions, rather it relies on the rate limiter to restrict attempts. Consequently, identified bypasses in the rate limiter permit unrestricted OTP code submissions within the codes lifetime. This allows attackers to perform brute force attacks which enable account takeover. Version 1.6.0 fixes the issue.

Affected products

VendorProductAffectedFixed
outline outline >= 0.86.0, < 1.6.0 —

References