CVE-2026-19867 PUBLISHED

Uncapped mention keys in user notification properties allow CPU exhaustion during post processing

Assigner: Mattermost
Reserved: 14.08.2026 Published: 16.10.2026 Updated: 16.10.2026

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

Metrics

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
CVSS Score: 4.3

Product Status

Vendor Mattermost
Product Mattermost
Versions Default: unaffected
  • affected from 11.10.0 to 11.10.0 (incl.)
  • affected from 11.9.0 to 11.9.1 (incl.)
  • affected from 11.8.0 to 11.8.5 (incl.)
  • affected from 11.7.0 to 11.7.10 (incl.)
  • Version 11.11.0 is unaffected
  • Version 11.10.1 is unaffected
  • Version 11.9.2 is unaffected
  • Version 11.8.6 is unaffected
  • Version 11.7.11 is unaffected

Solutions

Update Mattermost to versions 11.11.0, 11.10.1, 11.9.2, 11.8.6, 11.7.11 or higher.

Credits

  • CERT PL finder

References

Problem Types

  • CWE-770: Allocation of Resources Without Limits or Throttling CWE