{"cve":"CVE-2026-5740","nvd":{"published":"2026-05-22T11:16:23.163","modified":"2026-07-23T16:10:00.137","status":"Analyzed","description":"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 properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-789"],"references":["https://mattermost.com/security-updates"],"products":["mattermost:mattermost_server"],"source":"nvd","synced_at":"2026-10-19T22:36:28.938604137+00:00"},"epss":{"cve":"CVE-2026-5740","score":0.0034,"percentile":0.27522,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-w9m8-p4cc-4qj9","url":"https://osv.dev/vulnerability/GHSA-w9m8-p4cc-4qj9","summary":"Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation","modified":"2026-07-07T16:11:10.343209548Z","packages":[{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","ranges":[">=11.6.0 <11.6.1"],"fixed":["11.6.1"]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","ranges":[">=11.5.0 <11.5.4"],"fixed":["11.5.4"]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","ranges":[">=11.4.0 <11.4.5"],"fixed":["11.4.5"]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","ranges":[">=10.11.0 <10.11.15"],"fixed":["10.11.15"]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","ranges":["<8.0.0-20260410202636-17939826efa2"],"fixed":["8.0.0-20260410202636-17939826efa2"]}]},{"id":"GO-2026-5838","url":"https://osv.dev/vulnerability/GO-2026-5838","summary":"Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation in github.com/mattermost/mattermost-server","modified":"2026-07-07T16:01:34.665634742Z","packages":[{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server","purl":"pkg:golang/github.com/mattermost/mattermost-server","ranges":[">=10.11.0+incompatible <10.11.15+incompatible",">=11.4.0+incompatible <11.4.5+incompatible",">=11.5.0+incompatible <11.5.4+incompatible",">=11.6.0+incompatible <11.6.1+incompatible"],"fixed":["10.11.15+incompatible","11.4.5+incompatible","11.5.4+incompatible","11.6.1+incompatible"]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server/v5","purl":"pkg:golang/github.com/mattermost/mattermost-server/v5","ranges":["all versions"],"fixed":[]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost-server/v6","purl":"pkg:golang/github.com/mattermost/mattermost-server/v6","ranges":["all versions"],"fixed":[]},{"ecosystem":"Go","name":"github.com/mattermost/mattermost/server/v8","purl":"pkg:golang/github.com/mattermost/mattermost/server/v8","ranges":["<8.0.0-20260410202636-17939826efa2"],"fixed":["8.0.0-20260410202636-17939826efa2"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}