CVE-2026-6339 json
Missing request origin validation on burn-on-read reveal endpoint
published 2026-05-18 5 mo ago modified 2026-10-14 25 d ago also GHSA-xvcx-mgpc-5xh3 , GO-2026-5769 , EUVD-2026-30749
- cvss
- 4.3
- 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 1%
- public exploits
- 0
- none known
Summary
Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636
Patch / fix
- go github.com/mattermost/mattermost/server/v8 8.0.0-20260327001745-7a339a6438f5, 11.4.4, 11.5.2
- go github.com/mattermost/mattermost-server 5.3.2-0.20260327001745-7a339a6438f5, 11.4.4+incompatible, 11.5.2+incompatible
- Mattermost Mattermost 11.4.4, 11.5.2, 11.6.0
- govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1
opensuse advisories openSUSE-SU-2026:21483-1
CISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 5 mo ago
Exploit prediction
0.11% chance of exploitation in the next 30 days, higher than 1% 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:N/I:N/A:L |
| NVD | 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:N/I:N/A:L |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| go | github.com/mattermost/mattermost/server/v8 | >=11.5.0, <11.5.2 >=11.4.0, <11.4.4 <8.0.0-20260327001745-7a339a6438f5 |
11.5.2 11.4.4 8.0.0-20260327001745-7a339a6438f5 |
| go | github.com/mattermost/mattermost-server | <5.3.2-0.20260327001745-7a339a6438f5 >=11.4.0+incompatible, <11.4.4+incompatible >=11.5.0+incompatible, <11.5.2+incompatible |
5.3.2-0.20260327001745-7a339a6438f5 11.4.4+incompatible 11.5.2+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-346 Origin Validation Error
References
Sources
- CVE List CVE-2026-6339
- GitHub Advisory GHSA-xvcx-mgpc-5xh3
- NVD CVE-2026-6339
- OSV GO-2026-5769
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.