CVE-2026-4274 json
Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access
published 7mo ago modified 4mo ago also GHSA-g7fp-cqj5-x8hf , GO-2026-5393 , EUVD-2026-16162
- cvss
- 5.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.1%
- EPSS 0.1% chance of exploitation in 30 days, percentile 3%
- public exploits
- 0
- none known
Summary
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 restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574
Patch / fix
- 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
Is CVE-2026-4274 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 7mo ago
Exploit prediction
0.14% chance of exploitation in the next 30 days, higher than 3% of all scored CVEs (FIRST EPSS, 2026-11-09).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N |
| GitHub | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| go | github.com/mattermost/mattermost/server/v8 | >=11.4.0-rc1, <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-rc1+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-2026-4274
advisory
-
github.com
/mattermost/mattermost
package
-
github.com
/advisories/GHSA-g7fp-cqj5-x8hf
advisory
Sources
- CVE List CVE-2026-4274
- GitHub Advisory GHSA-g7fp-cqj5-x8hf
- NVD CVE-2026-4274
- OSV GO-2026-5393
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.