CVE-2026-33640: Outline has a rate limit bypass that allows brute force of email login OTP
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 Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-33640?
CVE-2026-33640 is classified as a high-severity vulnerability due to its potential for brute-force attacks on email login OTPs.
How do I fix CVE-2026-33640?
To mitigate CVE-2026-33640, upgrade Outline to version 1.6.0 or later.
What versions are affected by CVE-2026-33640?
CVE-2026-33640 affects Outline versions from 0.86.0 up to, but not including, 1.6.0.
What type of attack does CVE-2026-33640 enable?
CVE-2026-33640 enables brute-force attacks on the email OTP login mechanism.
Is CVE-2026-33640 specific to any platforms?
CVE-2026-33640 is specifically related to the Outline collaborative documentation service.