{"schema_version":"1.9.0","id":"GHSA-hxmp-pqch-c8mm","published":"2020-12-09T18:21:29Z","modified":"2026-09-10T03:49:00.422107261Z","aliases":["CVE-2020-26257","PYSEC-2020-236"],"summary":"Denial of service attack via incorrect parameters in Matrix Synapse","details":"### Impact\n\nA malicious or poorly-implemented homeserver can inject malformed events into a room by specifying a different room id in the path of a `/send_join`, `/send_leave`, `/invite` or `/exchange_third_party_invite` request.\n\nThis can lead to a denial of service in which future events will not be correctly sent to other servers over federation.\n\nThis affects any server which accepts federation requests from untrusted servers.\n\n### Patches\n\nIssue is resolved by https://github.com/matrix-org/synapse/pull/8776.\n\n### Workarounds\n\nHomeserver administrators could limit access to the federation API to trusted servers (for example via `federation_domain_whitelist`).","affected":[{"package":{"name":"matrix-synapse","ecosystem":"PyPI","purl":"pkg:pypi/matrix-synapse"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.23.1"}]}],"versions":["0.33.5","0.33.5.1","0.33.6","0.33.6rc1","0.33.7","0.33.7rc1","0.33.7rc2","0.33.8","0.33.8rc2","0.33.9","0.34.0","0.34.0.1","0.34.0rc1","0.34.0rc2","0.34.1.1","0.99.0","0.99.0rc1","0.99.0rc2","0.99.0rc3","0.99.0rc4","0.99.1","0.99.1.1","0.99.1rc1","0.99.1rc2","0.99.2","0.99.2rc1","0.99.3","0.99.3.1","0.99.3.2","0.99.3rc1","0.99.4","0.99.4rc1","0.99.5","0.99.5.1","0.99.5.2","0.99.5rc1","1.0.0","1.0.0rc1","1.0.0rc2","1.0.0rc3","1.1.0","1.1.0rc1","1.1.0rc2","1.10.0","1.10.0rc1","1.10.0rc2","1.10.0rc3","1.10.0rc5","1.10.1","1.11.0","1.11.0rc1","1.11.1","1.12.0","1.12.0rc1","1.12.1","1.12.1rc1","1.12.2","1.12.3","1.12.4","1.12.4rc1","1.13.0","1.13.0rc1","1.13.0rc2","1.13.0rc3","1.14.0","1.14.0rc1","1.14.0rc2","1.15.0","1.15.0rc1","1.15.1","1.15.2","1.16.0","1.16.0rc1","1.16.0rc2","1.16.1","1.17.0","1.17.0rc1","1.18.0","1.18.0rc1","1.18.0rc2","1.19.0","1.19.0rc1","1.19.1","1.19.1rc1","1.19.2","1.19.3","1.2.0","1.2.0rc1","1.2.0rc2","1.2.1","1.20.0","1.20.0rc1","1.20.0rc2","1.20.0rc3","1.20.0rc4","1.20.0rc5","1.20.1","1.21.0","1.21.0rc1","1.21.0rc2","1.21.0rc3","1.21.1","1.21.2","1.22.0","1.22.0rc1","1.22.0rc2","1.22.1","1.23.0","1.23.0rc1","1.3.0","1.3.0rc1","1.3.1","1.4.0","1.4.0rc1","1.4.0rc2","1.4.1","1.4.1rc1","1.5.0","1.5.0rc1","1.5.0rc2","1.5.1","1.6.0","1.6.0rc1","1.6.0rc2","1.6.1","1.7.0","1.7.0rc1","1.7.0rc2","1.7.1","1.7.2","1.7.3","1.8.0","1.8.0rc1","1.9.0","1.9.0.dev1","1.9.0.dev2","1.9.0rc1","1.9.1"],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2020/12/GHSA-hxmp-pqch-c8mm/GHSA-hxmp-pqch-c8mm.json"}}],"references":[{"type":"WEB","url":"https://github.com/matrix-org/synapse/security/advisories/GHSA-hxmp-pqch-c8mm"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2020-26257"},{"type":"WEB","url":"https://github.com/matrix-org/synapse/pull/8776"},{"type":"WEB","url":"https://github.com/matrix-org/synapse/commit/3ce2f303f15f6ac3dc352298972dc6e04d9b7a8b"},{"type":"WEB","url":"https://github.com/matrix-org/synapse/blob/develop/CHANGES.md#synapse-1231-2020-12-09"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2020-236.yaml"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/DBTIU3ZNBFWZ56V4X7JIAD33V5H2GOMC"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/QR4MMYZKX5N5GYGH4H5LBUUC5TLAFHI7"}],"database_specific":{"cwe_ids":["CWE-400","CWE-74","CWE-79"],"github_reviewed":true,"github_reviewed_at":"2020-12-09T18:21:17Z","nvd_published_at":"2020-12-09T19:15:00Z","severity":"HIGH"},"severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"}]}