CVE-2026-6339

medium

Published 2026-05-18 · Modified 2026-06-01

💬 Discuss on Community ✚ Propose mitigation

CVSS v3

4.3

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

CVSS v4 NEW

—

not yet in upstream

VIR risk

4.3

Description

Mattermost doesn't validate the X-Requested-With header on the burn-on-read reveal endpoint

Predictions

Exploit likelihood

53%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here with source_tier=community-verified.

Package impact

Ecosystem	Package	Vulnerable	Fixed
Go	github.com/mattermost/mattermost/server/v8	`>=11.5.0,<11.5.2`	`11.5.2`
Go	github.com/mattermost/mattermost/server/v8	`>=11.4.0,<11.4.4`	`11.4.4`
Go	github.com/mattermost/mattermost/server/v8	`<8.0.0-20260327001745-7a339a6438f5`	`8.0.0-20260327001745-7a339a6438f5`
Go	github.com/mattermost/mattermost-server	`<5.3.2-0.20260327001745-7a339a6438f5`	`5.3.2-0.20260327001745-7a339a6438f5`

Application impact

Vendor	Product	Versions	Fixed
mattermost	mattermost_server	`{"startIncluding":"11.4.0","endExcluding":"11.4.4"}`	`11.4.4`

References

CWEs

CWE-346

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.