CVE-2026-33640: Outline is a service that allows for collaborative documentation

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CRITICAL 9.8REMOTEUPGRADE

CVE-2026-33640 is a critical-severity flaw (CVSS 9.8) affecting outline. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 s

Why this priority

Critical severity
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 59%)
CISA exploited list	No
Weakness	CWE-307
Published	2026-03-26
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: getoutline

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-26 21:17 UTCPublished CVE record published
2026-06-17 10:37 UTCUpdated Record last modified

getoutline outline UPGRADE

Affected: >= 0.86.0 and < 1.6.0

Fixed in: 1.6.0

Safe to downgrade to: a release before 0.86.0

1. Check installed version

apt-cache policy outline || rpm -q outline || outline --version

2. UPGRADE to 1.6.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade outline

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade outline

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 0.86.0 (Debian / Ubuntu)

apt-cache madison outline sudo apt install outline=<VERSION_BEFORE_0.86.0> sudo apt-mark hold outline

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list outline sudo dnf downgrade outline-<VERSION_BEFORE_0.86.0> sudo dnf versionlock add outline

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

Fedora ELN · fonttools · FIXED · 4.68.0-1.eln159 · FEDORA-2026-37fa4b964c · source

sudo dnf upgrade --advisory=FEDORA-2026-37fa4b964c

Fedora 46 · fonttools · FIXED · 4.68.0-1.fc46 · FEDORA-2026-65d6c01c75 · source

sudo dnf upgrade --advisory=FEDORA-2026-65d6c01c75

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

Write-up: github.com/outline/outline/security/advisories/GHSA-cwhc-53hw-qqx6

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-33640?

outline: upgrade to 1.6.0. Exact commands for each OS are on this page.

Is CVE-2026-33640 being exploited?

CVE-2026-33640 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-33640 affect?

CVE-2026-33640 affects outline. Severity is critical (CVSS 9.8). 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 invalid

How urgent is CVE-2026-33640?

Priority 58/100. Critical severity; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-41649 HIGH 7.7 UPGRADE Outline is a service that allows for collaborative documentation
CVE-2026-44695 MEDIUM 5.8 UPGRADE Outline is a service that allows for collaborative documentation
CVE-2026-28506 MEDIUM 4.3 UPGRADE Outline is a service that allows for collaborative documentation
CVE-2026-24901 HIGH 8.1 UPGRADE Outline is a service that allows for collaborative documentation

References

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