{"items":[{"id":"NVI-00018333","kind":"vulnerability","title":"Mattermost doesn't validate the X-Requested-With header on the burn-on-read reveal endpoint","revision":1,"unknowns":["Customer inventory, deployment, reachability and exploitation have not been inspected."],"lifecycle":"active","identifiers":["GHSA-xvcx-mgpc-5xh3","CVE-2026-6339"],"plain_summary":"GitHub lists this reviewed advisory for github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost-server. 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-12581713c1675753f436af76f84bb04c"],"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":"2026-06-01T15:22:31.000Z","value":"4.3 medium","meaning":"GitHub source severity; exploitability and local consequence require separate evidence.","source_id":"sr-12581713c1675753f436af76f84bb04c"}],"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-12581713c1675753f436af76f84bb04c","url":"https://github.com/advisories/GHSA-xvcx-mgpc-5xh3","basis":"vendor_advisory","notes":"GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.","title":"GHSA-xvcx-mgpc-5xh3","publisher":"GitHub Advisory Database","observed_at":"2026-11-07T00:53:14.635Z"}],"affected_context":[{"certainty":"source_listed","source_ids":["sr-12581713c1675753f436af76f84bb04c"],"technology":"github.com/mattermost/mattermost/server/v8","known_exclusions":[],"conditions_summary":"Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636","public_affected_ranges":[">= 11.5.0, < 11.5.2"]},{"certainty":"source_listed","source_ids":["sr-12581713c1675753f436af76f84bb04c"],"technology":"github.com/mattermost/mattermost/server/v8","known_exclusions":[],"conditions_summary":"Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636","public_affected_ranges":[">= 11.4.0, < 11.4.4"]},{"certainty":"source_listed","source_ids":["sr-12581713c1675753f436af76f84bb04c"],"technology":"github.com/mattermost/mattermost/server/v8","known_exclusions":[],"conditions_summary":"Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636","public_affected_ranges":["< 8.0.0-20260327001745-7a339a6438f5"]},{"certainty":"source_listed","source_ids":["sr-12581713c1675753f436af76f84bb04c"],"technology":"github.com/mattermost/mattermost-server","known_exclusions":[],"conditions_summary":"Mattermost versions 11.5.x <= 11.5.1, 11.4.x <= 11.4.3 fail to validate the X-Requested-With header on the burn-on-read reveal endpoint which allows an authenticated channel member to force the reveal of a burn-on-read message without recipient consent via a crafted Markdown image tag.. Mattermost Advisory ID: MMSA-2026-00636","public_affected_ranges":["< 5.3.2-0.20260327001745-7a339a6438f5"]}],"null_published_at":"2026-11-07T07:07:39.815Z","source_updated_at":"2026-06-01T15:22:31.000Z","source_disclosed_at":"2026-05-18T09:31:48.000Z","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":"2026-11-07T00:53:14.635Z"}],"next_cursor":null,"snapshot_revision":"42594"}