CVE-2026-19603: Mattermost · Insertion of Sensitive Information Into Sent Data
Affects MattermostSource GCVE Database
Not known to be exploited · CVSS 4.3 Medium.
Data as of 29 Oct 2026, 21:16 UTC
Thin evidence
One scorer or none| CNA (Mattermost) | CVSS 3.1 | 4.3 |
|---|
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:NExploitation evidence
Disclosed: evidence found.
CVE published 16 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| Mattermost Mattermost | Affected
| Fixed in– |
Description
Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints, which allows an authenticated user to learn the channel ID of a private channel another user is actively viewing via the status endpoints, without being a member of that channel. Mattermost Advisory ID: MMSA-2026-00765