# CVE-2026-33640: Outline has a rate limit bypass that allows brute force of email login OTP

> Attackers can bypass rate limits to brute force email OTP codes, leading to account takeover in Outline collaborative documentation service.

- **Severity:** Critical 9.1 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 26 Mar 2026
- **Updated:** 1 Apr 2026
- **Also known as:** GHSA-cwhc-53hw-qqx6

## What is CVE-2026-33640?

CVE-2026-33640 is a critical vulnerability in outline, published on 26 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-307 (Improper Restriction of Excessive Authentication Attempts)

## Which versions are affected by CVE-2026-33640?

It affects 1 product.


Products: Getoutline Outline.

## How do I fix CVE-2026-33640?

No fix has been published for CVE-2026-33640 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-33640 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33640 exists.

## Other vulnerabilities in outline

- [CVE-2024-37829](https://insights.sbomify.com/CVE-2024-37829/): Auth bypass in n/a (high 8.8)
- [CVE-2023-54331](https://insights.sbomify.com/CVE-2023-54331/): Outline 1.6.0 - Unquoted Service Path (high 8.5)
- [CVE-2023-3532](https://insights.sbomify.com/CVE-2023-3532/): Cross-site Scripting (XSS) - Stored in outline/outline (high 8.5)
- [CVE-2026-24901](https://insights.sbomify.com/CVE-2026-24901/): Outline's IDOR allows unauthorized viewing and seizing of private deleted drafts (high 8.1)
- [CVE-2026-41649](https://insights.sbomify.com/CVE-2026-41649/): Outline has IDOR in document share creation that allows unauthorized access to private documents across workspaces (high 7.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33640 and fix it if it is affected.

What it is: CVE-2026-33640 is a critical vulnerability in outline, published on 26 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33640 exists.

Affected product: outline. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-33640/ (Markdown: https://insights.sbomify.com/CVE-2026-33640/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33640
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33640
- OSV: https://osv.dev/vulnerability/CVE-2026-33640

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33640/
Summaries are generated and may contain mistakes; the official description above is the record.