CVE-2026-4915

published 2026-05-25

CVE-2026-4915: Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment…

Priority P4 34 medium 6.5 CVSS 3.1

AV N AC L PR L UI N S U C N I N A H

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to filter nil elements from outgoing webhook attachment payloads before processing, which allows an authenticated user to cause a denial of service (server process termination) via a crafted webhook callback response containing a null attachment entry.. Mattermost Advisory ID: MMSA-2026-00641

Affected

13 ranges

Vendor	Product	Version range	Fixed in
github.com	mattermost_mattermost-server	>= 10.11.0 < 10.11.15	10.11.15
github.com	mattermost_mattermost-server	>= 11.4.0 < 11.4.5	11.4.5
github.com	mattermost_mattermost-server	>= 11.5.0 < 11.5.4	11.5.4
github.com	mattermost_mattermost-server	>= 11.6.0 < 11.6.1	11.6.1
github.com	mattermost_mattermost_server_v8	>= 0 < 8.0.0-20260407102538-faa7d75b4ea0	8.0.0-20260407102538-faa7d75b4ea0
mattermost	mattermost	10.11.0 – 10.11.14	—
mattermost	mattermost	11.4.0 – 11.4.4	—
mattermost	mattermost	11.5.0 – 11.5.3	—
mattermost	mattermost	11.6.0 – 11.6.0	—
mattermost	mattermost_server	>= 10.11.0 < 10.11.15	10.11.15
mattermost	mattermost_server	>= 11.4.0 < 11.4.5	11.4.5
mattermost	mattermost_server	>= 11.5.0 < 11.5.4	11.5.4
mattermost	mattermost_server	>= 11.6.0 < 11.6.1	11.6.1

CVSS provenance

nvd v3.1 6.5 MEDIUM CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

cvelistv5 v3.1 6.5 MEDIUM CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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CWE-754