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TI-2026-75226 Aliases CVE-2026-19867GHSA-9h79-c924-x83x

Mattermost mention key limits missing, enabling CPU exhaustion

Priority LOW 19CWE-770Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · Low
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-770.

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 11.10.0 fail to limit the number and size of mention keys stored in user notification properties (CWE-770). An authenticated user can store an oversized mention key list on their own profile, which slows post processing and consumes excessive CPU for other members of shared channels.

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

Description from the CNA

Mattermost versions 11.10.x <= 11.10.0, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10 fail to cap the number and size of mention keys stored in a user's notification properties, and to bound the quadratic multibyte-keyword matching performed for each post, which allows an authenticated user to degrade post-processing latency and consume excessive CPU on behalf of other members of any channel they share via storing an oversized notify_props.mention_keys list on their own profile.. Mattermost Advisory ID: MMSA-2026-00773

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00217 12th percentileScored 2026-11-07
Fix Fixed Mattermost (Mattermost): 11.11.0, 11.10.1, 11.9.2 +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
MattermostMattermost11.10.0 – 11.10.0; 11.9.0 – 11.9.1; 11.8.0 – 11.8.5; 11.7.0 – 11.7.1011.11.0, 11.10.1, 11.9.2, 11.8.6, 11.7.11Patch availableCNA
  • Mattermost VendorMattermost Affected 11.10.0 – 11.10.0; 11.9.0 – 11.9.1; 11.8.0 – 11.8.5; 11.7.0 – 11.7.10 Fixed in 11.11.0, 11.10.1, 11.9.2, 11.8.6, 11.7.11 Patch available CNA

CPE configurations NVD · 2

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 11.9.2VulnerableMattermost
cpe:2.3:a:mattermost:mattermost_server:11.10.0:*:*:*:*:*:*:*11.10.0VulnerableMattermost
  • 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 Vulnerable ·Mattermost
  • cpe:2.3:a:mattermost:mattermost_server:11.10.0:*:*:*:*:*:*:* Versions 11.10.0 Vulnerable ·Mattermost

Remediation

Upgrade Mattermost to 11.7.11, 11.8.6, 11.9.2, 11.10.1 or 11.11.0, the fixed versions for each affected branch, as described in Mattermost advisory MMSA-2026-00773.

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

  • Fix · CNA Mattermost (Mattermost) Fixed in 11.11.0, 11.10.1, 11.9.2, 11.8.6, 11.7.11

Timeline

  1. 2026-10-16 Threatist record created from CVE-2026-19867
  2. 2026-10-16 Alias added: GHSA-9h79-c924-x83x

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