{"action":"Upgrade matrix-synapse to 1.25.0 or later.","affected":[{"fixed":"1.25.0","introduced":"0.99.0"}],"component":"matrix-synapse","cve_ids":["CVE-2021-21274"],"ecosystem":"PyPI","epss":0.02164,"exploited":false,"fixed_versions":["1.25.0"],"ghsa_id":"GHSA-2hwx-mjrm-v3g8","id":"tcs_01M5KESPN16BHPH89AQPNXCG0Y","modified_at":"2026-09-10T03:49:14.211839612Z","published_at":"2021-03-01T19:34:54Z","references":["https://osv.dev/vulnerability/GHSA-2hwx-mjrm-v3g8","https://github.com/matrix-org/synapse/security/advisories/GHSA-2hwx-mjrm-v3g8","https://nvd.nist.gov/vuln/detail/CVE-2021-21274","https://github.com/matrix-org/synapse/pull/8950","https://github.com/matrix-org/synapse/commit/ff5c4da1289cb5e097902b3e55b771be342c29d6","https://github.com/matrix-org/synapse","https://github.com/matrix-org/synapse/releases/tag/v1.25.0","https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-132.yaml","https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY"],"severity":{"label":"medium","score":4.3},"sources":[{"source":"osv","source_id":"GHSA-2hwx-mjrm-v3g8","url":"https://osv.dev/vulnerability/GHSA-2hwx-mjrm-v3g8"}],"summary":"Denial of service attack via .well-known lookups"}