CVE-2026-16047Network attack vectorHinoki check available

Private-channel membership disclosure via board linking

Published Aug 17, 2026 · Updated Aug 17, 2026

Missing authorization in Mattermost before 10.11.22, 11.7.7, and 11.8.4 allows authenticated attackers to disclose private-channel membership. Boards create, patch, import, and bulk-create paths accept a caller-supplied channelId and link a board to that channel without verifying that the requester can read it. Any authenticated user who can invoke those board operations on the same team can test arbitrary channel IDs and infer whether private channels exist and who belongs to them; no message-content exposure is described.

CVSS severity4.3
Medium
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Missing authorization in Mattermost before 10.11.22, 11.7.7, and 11.8.4 allows authenticated attackers to disclose private-channel membership. Boards create, patch, import, and bulk-create paths accept a caller-supplied channelId and link a board to that channel without verifying that the requester can read it. Any authenticated user who can invoke those board operations on the same team can test arbitrary channel IDs and infer whether private channels exist and who belongs to them; no message-content exposure is described.

The record

CVE
CVE-2026-16047
Published
Aug 17, 2026
Updated
Aug 17, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-862, T1069
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 17, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 17, 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=10.11.0 <=10.11.21
  2. Affected versionversion=11.7.0 <=11.7.6
  3. Affected versionversion=11.8.0 <=11.8.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.11.0 <=10.11.21; version=11.7.0 <=11.7.6; version=11.8.0 <=11.8.3

Published CVSS scores

4.3MattermostCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/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-862Missing Authorization
T1069Permission Groups Discovery

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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