CVE-2026-16049

Summary

Mattermost Plugins versions <=11.8 10.20.11 11.5.7.0 The Mattermost GitLab plugin fails to verify channel permissions when processing API requests with a caller-supplied {{post_id}}, and fails to validate the {{web_url}} parameter against the configured GitLab instance, which allows an authenticated attacker to inject bot-authored messages containing arbitrary URLs into channels they do not have access to via the {{createIssue}} and {{attachCommentToIssue}} API endpoints. Mattermost Advisory ID: MMSA-2026-00673

Affected Software

VendorProductVersion RangeStatus
MattermostMattermost0 <= 10.20.11affected
MattermostMattermost0 <= 11.5.7affected
MattermostMattermost11.9.0unaffected
MattermostMattermost10.11.21unaffected
MattermostMattermost11.7.6unaffected

Weaknesses

  • CWE-862: CWE-862: Missing Authorization

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References