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Description

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to verify post ownership in the shared channel inbound sync handler, which allows an authenticated remote cluster to modify or delete posts authored by local users or other remotes via crafted sync messages referencing arbitrary post IDs in channels shared with that remote.. Mattermost Advisory ID: MMSA-2026-00689

PUBLISHED Reserved 2026-05-29 | Published 2026-07-13 | Updated 2026-07-14 | Assigner Mattermost




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

Problem types

CWE-639: Authorization Bypass Through User-Controlled Key

Product status

Default status
unaffected

11.7.0 (semver)
affected

11.6.0 (semver)
affected

10.11.0 (semver)
affected

11.8.0
unaffected

11.7.3
unaffected

11.6.5
unaffected

10.11.20
unaffected

Credits

ratrarity finder

References

mattermost.com/security-updates (MMSA-2026-00689) vendor-advisory

cve.org (CVE-2026-10103)

nvd.nist.gov (CVE-2026-10103)

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