EUVD-2026-16415
CVSS 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
3Description
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.
Analysis
Account takeover in Outline collaborative documentation service versions 0.86.0 through 1.5.x enables unauthenticated attackers to brute force Email OTP codes due to insufficient validation logic combined with rate limiter bypass. Attackers can submit unlimited OTP attempts within the code's validity window, compromising user accounts. …
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Remediation
Within 24 hours: Audit Outline deployment to confirm installed version (0.86.0-1.5.x affected); if confirmed, isolate or restrict network access to Outline instance pending mitigation. Within 7 days: Implement compensating controls (see below) and increase monitoring for suspicious OTP submission patterns and failed authentication attempts. …
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External POC / Exploit Code
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