CVE-2026-40205Network attack vector

Authentication bypass via OR-based OAuth2 scope validation

Published Aug 28, 2026 · Updated Aug 28, 2026

Improper authentication in OX Dovecot CE and Pro allows remote authenticated users to bypass OAuth2 scope policy through remote token validation. The OAuth2 passdb remote validation paths combine multiple required scopes with OR semantics, accepting a token when any one required scope is present. The issue requires multiple configured scopes, remote validation, and a token carrying only some required permissions; affected releases grant access that policy should reject.

CVSS severity5.9
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in OX Dovecot CE and Pro allows remote authenticated users to bypass OAuth2 scope policy through remote token validation. The OAuth2 passdb remote validation paths combine multiple required scopes with OR semantics, accepting a token when any one required scope is present. The issue requires multiple configured scopes, remote validation, and a token carrying only some required permissions; affected releases grant access that policy should reject.

The record

CVE
CVE-2026-40205
Published
Aug 28, 2026
Updated
Aug 28, 2026
Vendor
Open-Xchange GmbH
Product
OX Dovecot CE
Classifications
CWE-287, T1078
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 28, 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=2.3.11.2 <2.4.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Open-Xchange GmbH · OX Dovecot CEversion=2.3.11.2 <2.4.5
Open-Xchange GmbH · OX Dovecot Proversion=2.3.11.2 <2.3.22.2; version=3.0.0 <3.0.7; version=3.1.0 <3.1.6

Published CVSS scores

5.9Open-Xchange GmbHCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:N
5.9Red HatCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:N

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication
T1078Valid Accounts

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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