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CVE-2026-95666

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

Original 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

Mattermost

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "defaultStatus": "unaffected",
                    "product": "Mattermost",
                    "vendor": "Mattermost",
                    "versions": [
                        {
                            "lessThanOrEqual": "11.9.1",
                            "status": "affected",
                            "version": "11.9.0",
                            "versionType": "semver"
                        },
                        {
                            "lessThanOrEqual": "11.8.5",
                            "status": "affected",
                            "version": "11.8.0",
                            "versionType": "semver"
                        },
                        {
                            "lessThanOrEqual": "11.7.10",
                            "status": "affected",
                            "version": "11.7.0",
                            "versionType": "semver"
                        },
                        {
                            "lessThanOrEqual": "11.10.1",
                            "status": "affected",
                            "version": "11.10.0",
                            "versionType": "semver"
                        },
                        {
                            "version": "11.11.0",
                            "status": "unaffected"
                        },
                        {
                            "version": "11.9.2",
                            "status": "unaffected"
                        },
                        {
                            "version": "11.8.6",
                            "status": "unaffected"
                        },
                        {
                            "version": "11.7.11",
                            "status": "unaffected"
                        },
                        {
                            "version": "11.10.2",
                            "status": "unaffected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON