Medium severity4.3NVD Advisory· Published May 18, 2026· Updated May 18, 2026
CVE-2026-6339
CVE-2026-6339
Description
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
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
github.com/mattermost/mattermost/server/v8Go | >= 11.5.0, < 11.5.2 | 11.5.2 |
github.com/mattermost/mattermost/server/v8Go | >= 11.4.0, < 11.4.4 | 11.4.4 |
github.com/mattermost/mattermost/server/v8Go | < 8.0.0-20260327001745-7a339a6438f5 | 8.0.0-20260327001745-7a339a6438f5 |
github.com/mattermost/mattermost-serverGo | < 5.3.2-0.20260327001745-7a339a6438f5 | 5.3.2-0.20260327001745-7a339a6438f5 |
Affected products
4cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*+ 1 more
- cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*range: >=11.4.0,<11.4.4
- (no CPE)range: <=11.5.1, <=11.4.3
- ghsa-coords2 versionspkg:golang/github.com/mattermost/mattermost-serverpkg:golang/github.com/mattermost/mattermost/server/v8
< 5.3.2-0.20260327001745-7a339a6438f5+ 1 more
- (no CPE)range: < 5.3.2-0.20260327001745-7a339a6438f5
- (no CPE)range: >= 11.5.0, < 11.5.2
Patches
Vulnerability mechanics
References
4- github.com/advisories/GHSA-xvcx-mgpc-5xh3ghsaADVISORY
- mattermost.com/security-updatesnvdVendor AdvisoryWEB
- nvd.nist.gov/vuln/detail/CVE-2026-6339ghsaADVISORY
- github.com/mattermost/mattermost/commit/7a339a6438f5a4a5feba6b8de887f17a1378b207ghsaWEB
News mentions
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