CVE-2026-9693Network attack vectorHinoki check available

Private thread disclosure via stale memberships

Published Aug 17, 2026 · Updated Aug 18, 2026

Information disclosure in Mattermost before 10.11.21 and 11.7.6 allows remote authenticated users to read private thread data via the team threads API. When a user is removed from or leaves a team, Mattermost does not delete that user's thread membership records, so a later re-invite causes the API to honor stale membership state for private thread root posts and metadata. Exploitation requires an account that previously belonged to the team and is re-invited, and the exposed data is limited to private channel thread root content and related metadata rather than arbitrary channel access.

CVSS severity3.5
Low
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Information disclosure in Mattermost before 10.11.21 and 11.7.6 allows remote authenticated users to read private thread data via the team threads API. When a user is removed from or leaves a team, Mattermost does not delete that user's thread membership records, so a later re-invite causes the API to honor stale membership state for private thread root posts and metadata. Exploitation requires an account that previously belonged to the team and is re-invited, and the exposed data is limited to private channel thread root content and related metadata rather than arbitrary channel access.

The record

CVE
CVE-2026-9693
Published
Aug 17, 2026
Updated
Aug 18, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-459, T1213
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 17, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 18, 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 <=10.11.20
  2. Affected versionversion=11.7.0 <=11.7.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.11.0 <=10.11.20; version=11.7.0 <=11.7.5

Published CVSS scores

3.5Mattermost, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:R/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-459Incomplete Cleanup
T1213Data from Information Repositories

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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