CVE-2026-9693 — Mattermost thread memberships persist after team removal, exposing private channel thread metadata on re-invite
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
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.3% (30-day exploitation probability)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Mattermost Mattermost, Mattermost Mattermost Server).
- No fix documented in the sources: reduce exposure and monitor the vendor advisory.
- Exploitation requires user interaction: tighten email/web filtering and warn affected users.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Mattermost | Mattermost | ≥ 10.11.0 and ≤ 10.11.20≥ 11.7.0 and ≤ 11.7.5 | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Mattermost | Mattermost Server | ≥ 10.11.0 and < 10.11.21≥ 11.7.0 and < 11.7.6 | Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 3.5 | CVSS 3.1 | Low | 2.1 | 1.4 | responsibledisclosure@mattermost.com via NIST National Vulnerability Database |
| 3.5 | CVSS 3.1 | Low | — | — | Mattermost via CVE Program (cve.org) e CISA ADP |
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:N (score shown at the top: responsibledisclosure@mattermost.com) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · mattermost/mattermost
- SSVC assessment updated
- Record published
- CVSS changed · 3.5
- Source status changed · → Analyzed
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 15, 2026 – Oct 15, 2026
References
1 on the record
Elsewhere on this site
Related CVEs (same products)
- Medium CVE-2026-19621 Mattermost leaks interactive-message integration secrets to non-admin users via post-deletion events and thread reads 8h
- Medium CVE-2026-18799 Mattermost Server fails to restrict Slack import account binding, allowing team admins to forge posts as existing users 8h
- Medium CVE-2026-19076 Mattermost fails to reject OAuth application sessions in account type switch, allowing account takeover via bearer token 8h
- Medium CVE-2026-19600 Mattermost logs plaintext authentication tokens in debug-level server logs on failed auth attempts 8h
- Medium CVE-2026-18256 Private team metadata disclosure via the team search API 8h
- Medium CVE-2026-18223 Mattermost invitation tokens not bound to invited email address allowing unauthorized team and private channel access 8h
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No fixed version, patch or mitigation documented.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-9693 is "Mattermost thread memberships persist after team removal, exposing private channel thread metadata on re-invite", rated Low. It affects Mattermost (Mattermost); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 3.5 describes technical severity. EPSS 0.27% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
Comments
Moderated technical discussion. Read the community guidelines.
No comments yet.
Sign in or create an account to comment and suggest corrections.