{"action":"Upgrade matrix-synapse to 1.28.0rc1 or later.","affected":[{"fixed":"1.28.0rc1","introduced":"0"}],"component":"matrix-synapse","cve_ids":["CVE-2021-21392"],"ecosystem":"PyPI","epss":0.00944,"exploited":false,"fixed_versions":["1.28.0rc1"],"ghsa_id":"GHSA-5wrh-4jwv-5w78","id":"tcs_01M5KF1YDP8E64N241ADE9GTRE","modified_at":"2026-07-08T06:28:51.474360522Z","published_at":"2021-04-13T15:13:08Z","references":["https://osv.dev/vulnerability/GHSA-5wrh-4jwv-5w78","https://github.com/matrix-org/synapse/security/advisories/GHSA-5wrh-4jwv-5w78","https://nvd.nist.gov/vuln/detail/CVE-2021-21392","https://github.com/matrix-org/synapse/pull/9240","https://github.com/matrix-org/synapse/commit/4ca054a4eaa714d0befb4fc30b19a1131e52c9cc","https://github.com/matrix-org/synapse","https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-25.yaml","https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY","https://pypi.org/project/matrix-synapse"],"severity":{"label":"medium","score":6.3},"sources":[{"source":"osv","source_id":"GHSA-5wrh-4jwv-5w78","url":"https://osv.dev/vulnerability/GHSA-5wrh-4jwv-5w78"}],"summary":"Open redirect via transitional IPv6 addresses on dual-stack networks"}