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CVE-2026-9693

Mattermost thread memberships persist after team removal, exposing private channel thread metadata on re-invite

LOW

3.5

CVSS Score

Published: August 17, 2026 at 10:07 PM UTC

Updated: August 19, 2026 at 02:45 PM UTC

2 products affected across 1 vendorMattermost ServerMattermost

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Severity

LOW3.5

Exploit prediction

EPSS 0.3%

SSVC

No known exploit

Description

Mattermost versions 10.11.x <= 10.11.20, 11.7.x <= 11.7.5 Mattermost fails to remove thread membership records when a user is removed from or leaves a team, which allows a previously removed user who is later re-invited to the team to view private channel thread root post content and metadata via the team threads API.. Mattermost Advisory ID: MMSA-2026-00682

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Mattermost Server · Mattermost

95%

10.11.0 ≤ v < 10.11.2111.7.0 ≤ v < 11.7.6

Affected range stops below 10.11.21, so it looks safe — our inference, not a vendor statement

Affected range stops below 11.7.6, so it looks safe — our inference, not a vendor statement

Mattermost · Mattermost

60%

10.11.0 ≤ v ≤ 10.11.2011.7.0 ≤ v ≤ 11.7.510.11.0 11.7.0

Vendor states this is fixed in 10.11.21 (unaffected)

Vendor states this is fixed in 11.7.6 (unaffected)

Vendor states this is fixed in 11.9.0 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://mattermost.com/security-updates

References (1)

Vendor Advisory

Source: cverecord

https://mattermost.com/security-updates

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

3.5LOWMattermost

Attack Vector: NETWORK
Complexity: LOW
Privileges: LOW
User Interaction: REQUIRED
Scope: UNCHANGED
Confidentiality: LOW
Integrity: NONE
Availability: NONE

Vector?

Quick Info

StatusANALYZED

CWE

CWE-459

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