CVE-2026-3115Network attack vector

Guest user ID disclosure via omitted view restrictions

Published Mar 26, 2026 · Updated Mar 26, 2026

Incorrect authorization in affected Mattermost Server releases allows remote authenticated users to enumerate otherwise hidden user IDs. The group retrieval endpoint returns member IDs without applying the view restrictions that ordinarily limit a guest's user visibility. Affected releases are 10.11.0 through 10.11.10, 11.2.0 through 11.2.2, 11.3.0 through 11.3.1, and 11.4.0; guest access is sufficient, and exposure is limited to user identifiers.

CVSS severity4.3
Medium
EPSS probability0.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in affected Mattermost Server releases allows remote authenticated users to enumerate otherwise hidden user IDs. The group retrieval endpoint returns member IDs without applying the view restrictions that ordinarily limit a guest's user visibility. Affected releases are 10.11.0 through 10.11.10, 11.2.0 through 11.2.2, 11.3.0 through 11.3.1, and 11.4.0; guest access is sufficient, and exposure is limited to user identifiers.

The record

CVE
CVE-2026-3115
Published
Mar 26, 2026
Updated
Mar 26, 2026
Vendor
Mattermost
Product
Mattermost
Classifications
CWE-863, T1087
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 26, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 26, 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 <=10.11.10
  2. Affected versionversion=11.2.0 <=11.2.2
  3. Affected versionversion=11.3.0 <=11.3.1
  4. Affected versionversion=11.4.0 <=11.4.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Mattermost · Mattermostversion=10.11.0 <=10.11.10; version=11.2.0 <=11.2.2; version=11.3.0 <=11.3.1; version=11.4.0 <=11.4.0

Published CVSS scores

4.3Mattermost, Inc.CVSS: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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-863Incorrect Authorization
T1087Account Discovery

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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