Security officials have identified several vulnerabilities in Mattermost Server that could allow attackers to exploit unspecified security weaknesses. The issues were first reported on June 26, 2026, in four Mattermost security bulletins (MMSA‑2026‑00666, MMSA‑2026‑00681, MMSA‑2026‑00694, MMSA‑2026‑00695). Affected installations include Mattermost Server 10.11.x prior to 10.11.21, 11.6.x prior to 11.6.6, 11.7.x prior to 11.7.5, and 11.8.x prior to 11.8.2. The vulnerabilities could enable an attacker to trigger a security problem not defined by the vendor. System administrators are advised to consult the Mattermost security bulletins linked above for patches and to upgrade to the latest supported releases. Failure to update may expose the server to potential exploitation and compromise data integrity.
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