CVE-2026-40020Network attack vector

Folder spam via unenforced SETACL restriction

Published May 12, 2026 · Updated May 12, 2026

Improper access control in OX Dovecot Pro core 2.3.0 and earlier allows remote authenticated users to spam folders via IMAP SETACL. The SETACL handler writes the anyone identifier into a user's dovecot-acl file even when imap_acl_allow_anyone=no should reject it. A valid mailbox account and IMAP ACL support are required; the resulting folders appear to other users, but no unexpected mailbox access is gained.

CVSS severity3.1
Low
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in OX Dovecot Pro core 2.3.0 and earlier allows remote authenticated users to spam folders via IMAP SETACL. The SETACL handler writes the anyone identifier into a user's dovecot-acl file even when imap_acl_allow_anyone=no should reject it. A valid mailbox account and IMAP ACL support are required; the resulting folders appear to other users, but no unexpected mailbox access is gained.

The record

CVE
CVE-2026-40020
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Open-Xchange GmbH
Product
Dovecot Pro
Classifications
CWE-284
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 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 <=2.3.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Open-Xchange GmbH · Dovecot Proversion=0 <=2.3.0

Published CVSS scores

3.1Open-XchangeCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

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.

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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-284Improper Access Control

Public exploit references

No public exploit references are available in this record.

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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