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Unbounded post ID array in the bulk reactions endpoint allows denial of service

CVSS 3.1 4.3 MEDIUMCheck source for fixed versionsKEV status unknown

Historical advisory recorded 23 Oct 2026 15:48:27 UTC. Read the latest advisory.

cve-program · CVE-2026-95666

Published

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-95666

Published

Unbounded post ID array in the bulk reactions endpoint allows denial of service

Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 fail to limit the length of the post ID array accepted by the bulk reactions endpoint which allows an authenticated user to cause excessive database load via a crafted request to {{POST /api/v4/posts/ids/reactions}}.. Mattermost Advisory ID: MMSA-2026-00771

Source published
22 Sep 2026 13:11:13 UTC
Source modified
22 Sep 2026 13:57:00 UTC
Saved here
23 Oct 2026 15:48:27 UTC
Source terms
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Original source record · Cite this exact observation · Complete original publisher JSON

Source: cve-program · CVE Program Terms of Use. The publisher's wording is preserved. ChangeIntel groups the information and labels changes. The JSON record includes additional source fields.

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

ChangeIntel

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Sources read 15 Nov 23:13 UTC · 274 of 275 readable · 250 fully read · 18 waiting for GitHub's hourly limit · documentation 461/469 current