CVE-2026-33640CWE-307

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

Critical · published March 26, 2026

CVSS v4.0
9.1
EPSS
1%
Percentile
44.9
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v4.0
9.1 · CRITICAL
Vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
EPSS
0.00545 · 44.9th percentile
Weakness
CWE-307 · Improper Restriction of Excessive Authentication Attempts
Published
2026-03-26T20:56Z
EPSS history
Timeline
  • 26 MAR 20:56Z
    Outline has a rate limit bypass that allows brute force of email login OTP
    cvelistv5