CVE-2026-33640
Getoutline Outline 0.86.0 – 1.6.0
Raw 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:XSummary
CVE-2026-33640 is a critical-severity Improper Restriction of Excessive Authentication Attempts (CWE-307) vulnerability in Getoutline Outline. Its CVSS base score is 9.1 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Brute Force (T1110); ranked at the 38th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to AC-7 (Unsuccessful Logon Attempts) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-33640 is a high-severity vulnerability (CVSS 3.1 score of 9.8) affecting the Outline collaborative documentation service, specifically its Email OTP login flow for users not associated with an Identity Provider. In versions 0.86.0 through 1.5.x, Outline fails to invalidate OTP codes based on the number or frequency of invalid submissions, instead relying on a rate limiter with identified bypasses. This permits unrestricted OTP code submissions within the code's lifetime, enabling brute-force attacks that lead to account takeover (CWE-307: Improper Restriction of Excessive Authentication Attempts).
The vulnerability is exploitable remotely over the network by unauthenticated attackers (AV:N/AC:L/PR:N/UI:N) with no privileges or user interaction required. Attackers can brute-force Email OTP codes to gain unauthorized access to user accounts, achieving high impacts on confidentiality, integrity, and availability (C:H/I:H/A:H), including full account takeover.
Outline version 1.6.0 addresses the issue by fixing the OTP invalidation logic and rate limiter bypasses. Security practitioners should upgrade to this version immediately, as detailed in the official release notes (https://github.com/outline/outline/releases/tag/v1.6.0) and GitHub security advisory (https://github.com/outline/outline/security/advisories/GHSA-cwhc-53hw-qqx6).
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-16415
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 2 hardening rules · 1 OS baseline
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Mitigating Controls (NIST 800-53 r5) AI
AC-7 directly enforces limits on consecutive failed logons, structurally blocking brute-force exploitation of the weakness.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Authentication enforcement directly includes lockout, throttling, and MFA policies that prevent brute-force attempts.
Behavioral monitoring of authentication activity can detect excessive failed attempts after they occur.
Generating auth logs enables later detection or forensics but does not itself restrict attempts.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
CAPTCHA, account lock-out after repeated failures, and alerts on excessive attempts directly stop automated brute-force guessing of credentials.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
RHEL 7 (2 rules)
- V-204427 The Red Hat Enterprise Linux operating system must be configured to lock accounts for a minimum of 15 minutes after three unsuccessful logon attempts within a 15-minute timeframe. prevents CWE-307
- V-204428 The Red Hat Enterprise Linux operating system must lock the associated account after three unsuccessful root logon attempts are made within a 15-minute period. prevents CWE-307