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TI-2026-04507 Aliases CVE-2026-5163GHSA-8r89-8w26-cq32

Missing authorization check in AI message rewrite endpoint allows access to private thread content

Priority LOW 28CWE-862Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
High · None · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-862.

Summary

Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00205 10th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 11.6.0, 11.5.2github.com/mattermost/mattermost/server/v8 (Go): 11.5.2, 8.0.0-20260401090745-f4d1abe7e8f5+1 more product

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
MattermostMattermost11.5.0 – 11.5.111.6.0, 11.5.2Patch availableCNA
—github.com/mattermost/mattermost/server/v8 (Go)11.5.0 to before 11.5.211.5.2Patch availableGHSA-8r89-8w26-cq32
—github.com/mattermost/mattermost/server/v8 (Go)before 8.0.0-20260401090745-f4d1abe7e8f58.0.0-20260401090745-f4d1abe7e8f5Patch availableGHSA-8r89-8w26-cq32
—github.com/mattermost/mattermost-server (Go)before 5.3.2-0.20260401090745-f4d1abe7e8f55.3.2-0.20260401090745-f4d1abe7e8f5Patch availableGHSA-8r89-8w26-cq32
  • Mattermost VendorMattermost Affected 11.5.0 – 11.5.1 Fixed in 11.6.0, 11.5.2 Patch available CNA
  • github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected 11.5.0 to before 11.5.2 Fixed in 11.5.2 Patch available GHSA-8r89-8w26-cq32
  • github.com/mattermost/mattermost/server/v8 (Go) Vendor— Affected before 8.0.0-20260401090745-f4d1abe7e8f5 Fixed in 8.0.0-20260401090745-f4d1abe7e8f5 Patch available GHSA-8r89-8w26-cq32
  • github.com/mattermost/mattermost-server (Go) Vendor— Affected before 5.3.2-0.20260401090745-f4d1abe7e8f5 Fixed in 5.3.2-0.20260401090745-f4d1abe7e8f5 Patch available GHSA-8r89-8w26-cq32

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*11.5.0 to before 11.5.2VulnerableMattermost
  • cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:* Versions 11.5.0 to before 11.5.2 Vulnerable ·Mattermost

Remediation

  • Fix · CNA Mattermost (Mattermost) Fixed in 11.6.0, 11.5.2
  • Fix · GHSA-8r89-8w26-cq32 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 11.5.2 Advisory →
  • Fix · GHSA-8r89-8w26-cq32 github.com/mattermost/mattermost/server/v8 (Go) Fixed in 8.0.0-20260401090745-f4d1abe7e8f5 Advisory →
  • Fix · GHSA-8r89-8w26-cq32 github.com/mattermost/mattermost-server (Go) Fixed in 5.3.2-0.20260401090745-f4d1abe7e8f5 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-5163
  2. 2026-10-03 Alias added: GHSA-8r89-8w26-cq32

References

Advisory 2

Other 2

  • 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