Connected Workspaces: Malicious remote server can manipulate arbitrary user's status

published 2026-04-15 6 mo ago modified 2026-06-25 4 mo ago also GHSA-mxxh-fmjq-j6x4 , GO-2026-5522 , EUVD-2026-22873

cvss: 2.7; 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 6%
public exploits: 0; none known

Mattermost versions 10.11.x <= 10.11.12 fail to validate whether users were correctly owned by the correct Connected Workspace which allows a malicious remote server connected using the Conntexted Workspaces feature to change the displayed status of local users via the Connected Workspaces API.. Mattermost Advisory ID: MMSA-2026-00603

Patch / fix

fixed in 2 distros 1

go github.com/mattermost/mattermost-server 8.0.0-20260316060126-bc1a2b34b1f9
Mattermost Mattermost 10.11.13, 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-2026-27769 updated 2026-06-28 cvss 2.7

mattermost: connected workspaces: malicious remote server can manipulate arbitrary user's status

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: 6 mo ago (2026-04-15)

Exploit prediction

0.17% chance of exploitation in the next 30 days, higher than 6% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	2.7	CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:N
GitHub	3.1	2.7	CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
go	github.com/mattermost/mattermost-server	>=8.0.0-20250721062209-4952acea88ce, <8.0.0-20260316060126-bc1a2b34b1f9 all versions	8.0.0-20260316060126-bc1a2b34b1f9

Affected products

Mattermost Mattermost

Classification

Weakness

CWE-862 Missing Authorization

References

mattermost.com /security-updates
vendor-advisory, web
nvd.nist.gov /vuln/detail/CVE-2026-27769
advisory
github.com /mattermost/mattermost
package
github.com /advisories/GHSA-mxxh-fmjq-j6x4
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