CVE-2026-33640Public exploitNetwork attack vector

Account takeover via Email OTP rate-limit bypass

Published Mar 26, 2026 · Updated Mar 26, 2026

Authentication bypass in Outline 0.86.0 through 1.5.x allows remote attackers to take over Email OTP accounts via brute force. The /auth/email.callback handler neither limits invalid attempts nor invalidates the six-digit OTP, while rate-limit keys accept an unverified JWT id or, with a misconfigured proxy, spoofed X-Forwarded-For values. Attackers must know a non-IdP user’s email address and guess the code within its 10-minute lifetime; success grants the victim’s session and account access.

CVSS severity9.1
Critical
EPSS probability0.47%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Outline 0.86.0 through 1.5.x allows remote attackers to take over Email OTP accounts via brute force. The /auth/email.callback handler neither limits invalid attempts nor invalidates the six-digit OTP, while rate-limit keys accept an unverified JWT id or, with a misconfigured proxy, spoofed X-Forwarded-For values. Attackers must know a non-IdP user’s email address and guess the code within its 10-minute lifetime; success grants the victim’s session and account access.

The record

CVE
CVE-2026-33640
Published
Mar 26, 2026
Updated
Mar 26, 2026
Vendor
Outline
Product
Outline
Classifications
CWE-307, CAPEC-49, T1110.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 26, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 0.86.0, < 1.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Outline · Outlineversion=>= 0.86.0, < 1.6.0

Published CVSS scores

9.1GitHub, Inc.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
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-307Improper Restriction of Excessive Authentication Attempts
CAPEC-49Password Brute Forcing
T1110.001Brute Force: Password Guessing

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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