{"action":"Upgrade matrix-synapse to 1.27.0 or later.","affected":[{"fixed":"1.27.0","introduced":"0"}],"component":"matrix-synapse","cve_ids":["CVE-2021-21333"],"ecosystem":"PyPI","epss":0.01354,"exploited":false,"fixed_versions":["1.27.0"],"ghsa_id":"GHSA-c5f8-35qr-q4fm","id":"tcs_01M5KFC8EA2K70DF3YCKR3FQ1C","modified_at":"2026-07-08T06:27:41.174374736Z","published_at":"2021-03-26T19:53:04Z","references":["https://osv.dev/vulnerability/GHSA-c5f8-35qr-q4fm","https://github.com/matrix-org/synapse/security/advisories/GHSA-c5f8-35qr-q4fm","https://nvd.nist.gov/vuln/detail/CVE-2021-21333","https://github.com/matrix-org/synapse/pull/9200","https://github.com/matrix-org/synapse/commit/e54746bdf7d5c831eabe4dcea76a7626f1de73df","https://github.com/matrix-org/synapse","https://github.com/matrix-org/synapse/releases/tag/v1.27.0","https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-134.yaml","https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY"],"severity":{"label":"medium","score":6.1},"sources":[{"source":"osv","source_id":"GHSA-c5f8-35qr-q4fm","url":"https://osv.dev/vulnerability/GHSA-c5f8-35qr-q4fm"}],"summary":"HTML injection in email and account expiry notifications"}