Guest users can view group member IDs without respecting view restrictions

published 2026-03-26 7 mo ago modified 2026-06-25 4 mo ago also GHSA-mpc7-mm28-f6wq , GO-2026-5512 , EUVD-2026-16245

cvss: 4.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 15%
public exploits: 0; none known

Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to apply view restrictions when retrieving group member IDs, which allows authenticated guest users to enumerate user IDs outside their allowed visibility scope via the group retrieval endpoint.. Mattermost Advisory ID: MMSA-2026-00594

Patch / fix

fixed in 3 distros 1

go github.com/mattermost/mattermost/server/v8 8.0.0-20260217110922-b7d4a1f1f59b, 10.11.11, 11.2.3, 11.3.2, 11.4.1
go github.com/mattermost/mattermost-server 10.11.11+incompatible, 11.2.3+incompatible, 11.3.2+incompatible, 11.4.1+incompatible
Mattermost Mattermost 10.11.11, 11.2.3, 11.3.2, 11.4.1, 11.5.0

govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-3115 updated 2026-06-28 cvss 4.3

mattermost: Mattermost: Information disclosure via group retrieval endpoint

Red Hat All currently supported Red Hat products
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 7 mo ago (2026-03-26)

Exploit prediction

0.24% chance of exploitation in the next 30 days, higher than 15% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
GitHub	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

Affected packages

ecosystem	package	affected	fixed in
go	github.com/mattermost/mattermost/server/v8	>=11.4.0, <11.4.1 >=11.3.0-rc1, <11.3.2 >=11.2.0-rc1, <11.2.3 >=10.11.0-rc1, <10.11.11 >=8.0.0-20260105080200-d27a2195068d, <8.0.0-20260217110922-b7d4a1f1f59b	11.4.1 11.3.2 11.2.3 10.11.11 8.0.0-20260217110922-b7d4a1f1f59b
go	github.com/mattermost/mattermost-server	>=10.11.0-rc1+incompatible, <10.11.11+incompatible >=11.2.0-rc1+incompatible, <11.2.3+incompatible >=11.3.0-rc1+incompatible, <11.3.2+incompatible >=11.4.0+incompatible, <11.4.1+incompatible	10.11.11+incompatible 11.2.3+incompatible 11.3.2+incompatible 11.4.1+incompatible
go	github.com/mattermost/mattermost-server/v5	all versions	no fix listed
go	github.com/mattermost/mattermost-server/v6	all versions	no fix listed

Affected products

Mattermost Mattermost

Classification

Weakness

CWE-863 Incorrect Authorization

References

mattermost.com /security-updates
vendor-advisory, web
nvd.nist.gov /vuln/detail/CVE-2026-3115
advisory
github.com /mattermost/mattermost
package
github.com /advisories/GHSA-mpc7-mm28-f6wq
advisory

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary