Brute Force Vulnerability in Outline Documentation Service
CVE-2026-33640

9.1CRITICAL

Key Information:

Vendor

Outline

Status
Outline
Vendor
CVE Published:
26 March 2026

What is CVE-2026-33640?

Outline, a collaborative documentation service, is vulnerable due to its Email OTP login mechanism, which does not invalidate OTP codes following multiple invalid attempts. Instead, it relies on a rate limiter to control submission attempts. This design flaw allows attackers to exploit bypasses in the rate limiter, potentially enabling them to submit numerous OTP codes within the valid time frame. This vulnerability poses a significant risk of account takeover for users. The issue has been addressed and resolved in Outline version 1.6.0.

Affected Version(s)

outline >= 0.86.0, < 1.6.0

References

https://github.com/outline/outline/security/advisories/GH...
x_refsource_CONFIRM
https://github.com/outline/outline/releases/tag/v1.6.0
x_refsource_MISC

CVSS V4

Score:
9.1
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

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