Origin Validation Error Affecting github.com/mattermost/mattermost/server/channels/api4 package, versions >=11.4.0-rc1 <11.4.4>=11.5.0-rc1 <11.5.2-rc3
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-GOLANG-GITHUBCOMMATTERMOSTMATTERMOSTSERVERCHANNELSAPI4-16755260
- published19 May 2026
- disclosed18 May 2026
- creditgame0v3r
Introduced: 18 May 2026
NewCVE-2026-6339 (opens in a new tab)How to fix?
Upgrade github.com/mattermost/mattermost/server/channels/api4 to version 11.4.4, 11.5.2-rc3 or higher.
Overview
Affected versions of this package are vulnerable to Origin Validation Error via the burn-on-read reveal endpoint due to missing validation of the X-Requested-With header. An attacker can force the unauthorized reveal of a burn-on-read message without recipient consent by sending a crafted Markdown image tag as an authenticated channel member.