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TI-2026-75223 Aliases CVE-2026-19603GHSA-7ggq-hqj4-w5vc

Private channel ID disclosure via Mattermost user status endpoints

Priority LOW 19CWE-201Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Information disclosure
Confidentiality · integrity · availability
Low · None · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-201.

Summary

Mattermost versions from 11.7.0 through 11.7.10, from 11.8.0 through 11.8.5, from 11.9.0 through 11.9.1, and from 11.10.0 through 11.10.1 fail to sanitize the active channel field returned by the user status API endpoints. An authenticated user can learn the channel ID of a private channel that another user is actively viewing, without being a member of that channel, as CWE-201 describes.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Description from the CNA

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

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.0018 7th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 11.11.0, 11.9.2, 11.8.6 +2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
MattermostMattermost11.9.0 – 11.9.1; 11.8.0 – 11.8.5; 11.7.0 – 11.7.10; 11.10.0 – 11.10.111.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2Patch availableCNA
  • Mattermost VendorMattermost Affected 11.9.0 – 11.9.1; 11.8.0 – 11.8.5; 11.7.0 – 11.7.10; 11.10.0 – 11.10.1 Fixed in 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*11.7.0 to before 11.7.11; 11.8.0 to before 11.8.6; 11.9.0 to before 11.9.2; 11.10.0 to before 11.10.2VulnerableMattermost
  • cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 11.7.0 to before 11.7.11; 11.8.0 to before 11.8.6; 11.9.0 to before 11.9.2; 11.10.0 to before 11.10.2 Vulnerable ·Mattermost

Remediation

Upgrade Mattermost to 11.7.11, 11.8.6, 11.9.2, 11.10.2 or 11.11.0, which fix the flaw. Mattermost advisory MMSA-2026-00765 covers this issue.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

  • Fix · CNA Mattermost (Mattermost) Fixed in 11.11.0, 11.9.2, 11.8.6, 11.7.11, 11.10.2

Timeline

  1. 2026-10-16 Threatist record created from CVE-2026-19603
  2. 2026-10-16 Alias added: GHSA-7ggq-hqj4-w5vc

References

Advisory 1

  • TI-2025-18933 Arbitrary file read in Mattermost Boards via import & export board archive CVSS 3.1CRITICAL 9.9
  • TI-2025-04465 Path Traversal Leading to RCE by Any Authenticated Mattermost User CVSS 3.1CRITICAL 9.9
  • TI-2017-14068 An issue was discovered in Mattermost Server before 3.6.2. CVSS 3.1CRITICAL 9.8
  • TI-2017-14060 An issue was discovered in Mattermost Server before 3.8.2, 3.7.5, and 3.6.7. CVSS 3.1CRITICAL 9.8
  • TI-2017-14048 An issue was discovered in Mattermost Server before 4.1.0, 4.0.4, and 3.10.3. CVSS 3.1CRITICAL 9.8
  • TI-2025-14360 Arbitrary file read via block duplication in Mattermost Boards CVSS 3.1CRITICAL 9.9
See all 505 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences