{"items":[{"id":"NVI-00017817","kind":"vulnerability","title":"Mattermost doesn't properly validate msgpack-encoded WebSocket frames before memory allocation","revision":1,"unknowns":["Customer inventory, deployment, reachability and exploitation have not been inspected."],"lifecycle":"active","identifiers":["GHSA-w9m8-p4cc-4qj9","CVE-2026-5740"],"plain_summary":"GitHub lists this reviewed advisory for github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server, github.com/mattermost/mattermost-server, github.com/mattermost/mattermost/server/v8. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.","review_status":"source_listed","control_topics":[],"public_actions":[{"summary":"Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.","source_ids":["sr-6db844055ae9b7c896915cc858d34088"],"action_type":"investigate","limitations":"Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system.","current_supported_target":null}],"schema_version":"1.1.0","source_metrics":[{"kind":"CVSS","as_of":"2026-06-29T22:52:00.000Z","value":"7.5 high","meaning":"GitHub source severity; exploitability and local consequence require separate evidence.","source_id":"sr-6db844055ae9b7c896915cc858d34088"}],"why_it_matters":"Published affected context helps an owner decide what evidence to gather. This report has not examined your application.","related_sources":[{"id":"sr-6db844055ae9b7c896915cc858d34088","url":"https://github.com/advisories/GHSA-w9m8-p4cc-4qj9","basis":"vendor_advisory","notes":"GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.","title":"GHSA-w9m8-p4cc-4qj9","publisher":"GitHub Advisory Database","observed_at":"2026-11-05T19:05:04.022Z"}],"affected_context":[{"certainty":"source_listed","source_ids":["sr-6db844055ae9b7c896915cc858d34088"],"technology":"github.com/mattermost/mattermost-server","known_exclusions":[],"conditions_summary":"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","public_affected_ranges":["= 11.6.0"]},{"certainty":"source_listed","source_ids":["sr-6db844055ae9b7c896915cc858d34088"],"technology":"github.com/mattermost/mattermost-server","known_exclusions":[],"conditions_summary":"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","public_affected_ranges":[">= 11.5.0, < 11.5.4"]},{"certainty":"source_listed","source_ids":["sr-6db844055ae9b7c896915cc858d34088"],"technology":"github.com/mattermost/mattermost-server","known_exclusions":[],"conditions_summary":"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","public_affected_ranges":[">= 11.4.0, < 11.4.5"]},{"certainty":"source_listed","source_ids":["sr-6db844055ae9b7c896915cc858d34088"],"technology":"github.com/mattermost/mattermost-server","known_exclusions":[],"conditions_summary":"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","public_affected_ranges":[">= 10.11.0, < 10.11.15"]},{"certainty":"source_listed","source_ids":["sr-6db844055ae9b7c896915cc858d34088"],"technology":"github.com/mattermost/mattermost/server/v8","known_exclusions":[],"conditions_summary":"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","public_affected_ranges":["< 8.0.0-20260410202636-17939826efa2"]}],"null_published_at":"2026-11-05T19:10:21.471Z","source_updated_at":"2026-06-29T22:52:00.000Z","source_disclosed_at":"2026-05-26T13:30:15.000Z","is_synthetic_fixture":false,"null_last_reviewed_at":null,"public_change_summary":"First indexed by Null; source disclosure date is shown separately.","null_first_observed_at":"2026-11-05T19:05:04.022Z"}],"next_cursor":null,"snapshot_revision":"42594"}