Mattermost Server allows attackers to gain privileges by accessing unintended API endpoints with users' credentials

published 2020-06-19 6y ago modified 2026-06-17 4mo ago also GHSA-g78f-6xq7-rrhq , GO-2025-4200 , EUVD-2017-9975

cvss: 9.8; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.2%; EPSS 1.2% chance of exploitation in 30 days, percentile 68%
public exploits: 0; none known

An issue was discovered in Mattermost Server before 4.3.0, 4.2.1, and 4.1.2. It allows attackers to gain privileges by accessing unintended API endpoints on a user's behalf.

Patch / fix

fixed in 2 distros 2

go github.com/mattermost/mattermost-server 4.1.2, 4.1.2+incompatible, 4.2.1, 4.2.1+incompatible, 4.3.0, 4.3.0+incompatible
mattermost mattermost_server 4.1.2, 4.2.1

suse opensuse

govulncheck-vulndb openSUSE Leap 15.6 0.0.20251230T014957-150000.1.134.1

suse advisories SUSE-SU-2026:0037-1

govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1

opensuse advisories openSUSE-SU-2026:21483-1

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Exploit prediction

1.18% chance of exploitation in the next 30 days, higher than 68% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by	version	score	vector
NVD	3.1	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD	2.0	7.5	AV:N/AC:L/Au:N/C:P/I:P/A:P
GitHub	3.1	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem	package	affected	fixed in
go	github.com/mattermost/mattermost-server	<4.1.2 >=4.2.0-rc1, <4.2.1 >=4.3.0-rc1, <4.3.0 <4.1.2+incompatible >=4.2.0-rc1+incompatible, <4.2.1+incompatible >=4.3.0-rc1+incompatible, <4.3.0+incompatible	4.1.2 4.2.1 4.3.0 4.1.2+incompatible 4.2.1+incompatible 4.3.0+incompatible

Classification

Weakness

CWE-269 Improper Privilege Management

References

mattermost.com /security-updates/
vendor-advisory
nvd.nist.gov /vuln/detail/CVE-2017-18885
advisory
github.com /mattermost/mattermost
package
mattermost.com /security-updates
web
github.com /advisories/GHSA-g78f-6xq7-rrhq
advisory

Sources

Fencer Intel 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.