{"id":"PYSEC-2026-846","summary":"Matrix Synapse DoS","details":"Matrix Synapse before 0.28.1 is prone to a denial of service flaw where malicious events injected with depth = 2\u003csup\u003e63\u003c/sup\u003e - 1 render rooms unusable, related to `federation/federation_base.py` and `handlers/message.py`, as exploited in the wild in April 2018.","aliases":["CVE-2018-10657","GHSA-vmcc-4p4x-x7wg"],"modified":"2026-07-07T11:45:24.424863794Z","published":"2026-07-06T08:03:24.087354Z","references":[{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2018-10657"},{"type":"WEB","url":"https://github.com/matrix-org/synapse/commit/33f469ba19586bbafa0cf2c7d7c35463bdab87eb"},{"type":"WEB","url":"https://docs.google.com/document/d/1I3fi2S-XnpO45qrpCsowZv8P8dHcNZ4fsBsbOW7KABI/edit#heading=h.fj95ykuss7s1"},{"type":"PACKAGE","url":"https://github.com/matrix-org/synapse"},{"type":"WEB","url":"https://matrix.org/blog/2018/05/01/security-update-synapse-0-28-1"},{"type":"PACKAGE","url":"https://pypi.org/project/matrix-synapse"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-vmcc-4p4x-x7wg"}],"affected":[{"package":{"name":"matrix-synapse","ecosystem":"PyPI","purl":"pkg:pypi/matrix-synapse"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.28.1"}]}],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/matrix-synapse/PYSEC-2026-846.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:N/I:N/A:H"}]}