{"id":"PYSEC-2026-664","summary":"Matrix Synapse Security Filtering Flaw","details":"The `on_get_missing_events` function in handlers/federation.py in Matrix Synapse before 0.31.1 has a security bug in the get_missing_events federation API where event visibility rules were not applied correctly.","aliases":["CVE-2018-12291","GHSA-v8wm-g9f2-xjv4"],"modified":"2026-07-06T08:00:53.308300896Z","published":"2026-07-02T14:13:24.881978Z","references":[{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2018-12291"},{"type":"WEB","url":"https://github.com/matrix-org/synapse/pull/3371"},{"type":"WEB","url":"https://github.com/matrix-org/synapse/commit/0834b49c6a9b6c597a154d4b2dfcf8fff90699ec"},{"type":"PACKAGE","url":"https://github.com/matrix-org/synapse"},{"type":"WEB","url":"https://github.com/matrix-org/synapse/releases/tag/v0.31.1"},{"type":"PACKAGE","url":"https://pypi.org/project/matrix-synapse"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-v8wm-g9f2-xjv4"}],"affected":[{"package":{"name":"matrix-synapse","ecosystem":"PyPI","purl":"pkg:pypi/matrix-synapse"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.31.1"}]}],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/matrix-synapse/PYSEC-2026-664.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"}]}