CVE-2026-33640
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedOutline 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceOutline's Email OTP authentication flow does not invalidate OTP codes after a threshold of invalid submissions, relying solely on a rate limiter that can be bypassed. This allows attackers to perform unlimited brute force attempts within the OTP's validity window, enabling account takeover.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 0.86.0, < 1.6.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed Outline versionDetermine the running version of Outline (e.g., via admin UI, API endpoint, package.json, or Docker image tag). Compare it to the affected range: >= 0.86.0 and < 1.6.0.Affected if The installed version falls within >= 0.86.0 and < 1.6.0
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Verify Email OTP authentication is enabledConfirm that Email OTP is configured as an authentication method in the Outline instance (check authentication settings in admin panel or configuration files).Affected if Email OTP authentication is enabled in the environment
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Confirm rate limiter behaviorTest the OTP submission endpoint to determine if the rate limiter can be bypassed or allows unlimited attempts within the OTP validity window.Affected if The rate limiter does not block or invalidate OTP codes after multiple failed attempts, allowing unlimited brute force attempts
The environment is affected if running Outline version >= 0.86.0 and < 1.6.0 with Email OTP authentication enabled, and the rate limiter can be bypassed to allow unlimited OTP submission attempts.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped1.6.0
Upgrade to Outline version 1.6.0 or later, which implements OTP code invalidation based on the number of invalid submission attempts.
1.6.0
- Verify current Outline version by checking the running container or application metadata
- Review the Outline upgrade documentation for your deployment method (Docker, Kubernetes, etc.)
- Back up the Outline database and configuration files before upgrading
- Pull the updated Outline 1.6.0 container image or download the new release
- Stop the current Outline instance
- Apply the upgrade following Outlines official upgrade procedure
- Verify the upgrade was successful by checking the application version
- Test the Email OTP login flow to confirm the fix is working
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-33640 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-33640 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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