{"id":"CVE-2021-21332","aliases":["DEBIAN-CVE-2021-21332","EUVD-2021-0125","GHSA-246w-56m2-5899","PYSEC-2021-133","UBUNTU-CVE-2021-21332"],"status":"published","title":"Cross-site scripting (XSS) vulnerability in the password reset endpoint","description":"Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.","severity":{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.01221,"percentile":0.6908,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-79"],"published":"2021-03-26T19:52:54Z","modified":"2026-10-20T10:53:33Z","fixes":[{"ecosystem":"PyPI","package":"matrix-synapse","fixed_in":["1.27.0"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"matrix-synapse","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.27.0"}]}]},{"source":"osv","ecosystem":"PyPI","package":"matrix-synapse","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.27.0"}]}],"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","1.23.1","1.24.0","1.24.0rc1","1.24.0rc2","1.25.0","1.25.0rc1","1.26.0","1.26.0rc1","1.26.0rc2","1.27.0rc1","1.27.0rc2","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"]},{"source":"osv","ecosystem":"PyPI","package":"matrix-synapse","ranges":[{"type":"GIT","events":[{"introduced":"0"},{"fixed":"e54746bdf7d5c831eabe4dcea76a7626f1de73df"}]},{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.27.0"}]}],"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","1.23.1","1.24.0","1.24.0rc1","1.24.0rc2","1.25.0","1.25.0rc1","1.26.0","1.26.0rc1","1.26.0rc2","1.27.0rc1","1.27.0rc2","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"]},{"source":"osv","ecosystem":"Ubuntu:Pro:18.04:LTS","package":"matrix-synapse","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.19.2+dfsg-6","0.24.0+dfsg-1","0.24.0+dfsg-1ubuntu0.1~esm1","0.24.0+dfsg-1ubuntu0.1~esm4"]},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"matrix-synapse","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.3.0-1","1.4.0-1","1.5.0-1","1.5.1-1","1.6.0-1","1.6.1-1","1.7.0-2","1.7.1-1","1.7.2-1","1.7.3-1","1.8.0-1","1.9.0-1","1.9.1-1","1.10.0-1","1.10.0-2","1.11.0-1","1.11.0-1ubuntu0.1~esm2"]}],"products":[{"vendor":"element-hq","product":"synapse"},{"vendor":"fedoraproject","product":"fedora"},{"vendor":"matrix","product":"synapse"},{"vendor":"matrix-org","product":"synapse"}],"references":[{"url":"https://github.com/matrix-org/synapse/security/advisories/GHSA-246w-56m2-5899","tags":["x_refsource_CONFIRM","x_transferred","Third Party Advisory","advisory","web","report"]},{"url":"https://github.com/matrix-org/synapse/releases/tag/v1.27.0","tags":["x_refsource_MISC","x_transferred","Third Party Advisory","advisory","web","report"]},{"url":"https://github.com/matrix-org/synapse/pull/9200","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web"]},{"url":"https://github.com/matrix-org/synapse/commit/e54746bdf7d5c831eabe4dcea76a7626f1de73df","tags":["x_refsource_MISC","x_transferred","Patch","Third Party Advisory","fix","web"]},{"url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/","tags":["vendor-advisory","x_refsource_FEDORA","x_transferred","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21332","tags":["advisory"]},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-133.yaml","tags":["web"]},{"url":"https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY","tags":["web"]},{"url":"https://github.com/advisories/GHSA-246w-56m2-5899"},{"url":"https://security-tracker.debian.org/tracker/CVE-2021-21332","tags":["advisory"]},{"url":"https://github.com/matrix-org/synapse","tags":["package"]},{"url":"https://ubuntu.com/security/CVE-2021-21332","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2021-21332","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2021-21332","title":"Cross-site scripting (XSS) vulnerability in the password reset endpoint","description":"Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.","status":"published","published":"2021-03-26T19:55:17Z","modified":"2024-08-03T18:09:15.157Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T14:33:00.137099Z"}],"euvd":[{"id":"EUVD-2021-0125","description":"Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.","status":"published","published":"2021-03-26T19:55:17Z","modified":"2024-08-03T18:09:15Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium"}],"updated_at":"2026-11-03T03:25:06.913643Z"}],"ghsa":[{"id":"GHSA-246w-56m2-5899","title":"Cross-site scripting (XSS) vulnerability in the password reset endpoint","description":"### Impact\nThe password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains.\n\n### Patches\nThis is fixed in #9200.\n\n### Workarounds\nDepending on the needs and configuration of the homeserver a few options are available:\n\n1. Password resets can be disabled by delegating email to a third-party service (via the `account_threepid_delegates.email` setting) or disabling email (by not configuring the `email` setting).\n\n2. If the homeserver is not configured to use passwords (via the `password_config.enabled` setting) then the affected endpoint can be blocked at a reverse proxy:\n\n    * `/_synapse/client/password_reset/email/submit_token`\n\n3. The `password_reset_confirmation.html` template can be overridden with a custom template that manually escapes the variables using [JInja2's `escape` filter](https://jinja.palletsprojects.com/en/2.11.x/templates/#escape). See the `email.template_dir` setting.","status":"published","published":"2021-03-26T19:52:54Z","modified":"2024-09-30T20:30:22Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium"},{"version":"4.0","score":5.1,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N","level":"medium"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T14:38:07.852618Z"}],"nvd":[{"id":"CVE-2021-21332","description":"Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.","status":"published","published":"2021-03-26T20:15:11.843Z","modified":"2026-06-17T03:35:18.94Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium","assessor":"secondary"},{"version":"3.1","score":8.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"high","assessor":"primary"},{"version":"2.0","score":4.3,"vector":"AV:N/AC:M/Au:N/C:N/I:P/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T14:06:51.197859Z"}],"osv":[{"id":"CVE-2021-21332","description":"Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.","status":"published","published":"2021-03-26T20:15:11.843Z","modified":"2026-10-20T10:53:33.400999484Z","cvss":[{"version":"3.1","score":8.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"high"}],"updated_at":"2026-11-02T15:44:18.004149Z"},{"id":"DEBIAN-CVE-2021-21332","description":"Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.","status":"withdrawn","published":"2021-03-26T20:15:11.843Z","modified":"2026-08-11T20:49:51.55897171Z","cvss":[{"version":"3.1","score":8.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"high"}],"updated_at":"2026-11-02T15:45:34.637046Z"},{"id":"GHSA-246w-56m2-5899","title":"Cross-site scripting (XSS) vulnerability in the password reset endpoint","description":"### Impact\nThe password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains.\n\n### Patches\nThis is fixed in #9200.\n\n### Workarounds\nDepending on the needs and configuration of the homeserver a few options are available:\n\n1. Password resets can be disabled by delegating email to a third-party service (via the `account_threepid_delegates.email` setting) or disabling email (by not configuring the `email` setting).\n\n2. If the homeserver is not configured to use passwords (via the `password_config.enabled` setting) then the affected endpoint can be blocked at a reverse proxy:\n\n    * `/_synapse/client/password_reset/email/submit_token`\n\n3. The `password_reset_confirmation.html` template can be overridden with a custom template that manually escapes the variables using [JInja2's `escape` filter](https://jinja.palletsprojects.com/en/2.11.x/templates/#escape). See the `email.template_dir` setting.","status":"published","published":"2021-03-26T19:52:54Z","modified":"2026-07-08T06:27:41.588536149Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium"},{"version":"4.0","score":5.1,"vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N","level":"medium"}],"cwes":["CWE-79"],"updated_at":"2026-11-02T15:46:33.520522Z"},{"id":"UBUNTU-CVE-2021-21332","description":"Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.","status":"published","published":"2021-03-26T20:15:00Z","modified":"2025-09-08T16:46:57Z","cvss":[{"version":"3.1","score":6.9,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"medium"},{"version":"3.1","score":8.2,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N","level":"high"}],"updated_at":"2026-11-02T15:54:26.29421Z"},{"id":"PYSEC-2021-133","description":"Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.27.0, the password reset endpoint served via Synapse was vulnerable to cross-site scripting (XSS) attacks. The impact depends on the configuration of the domain that Synapse is deployed on, but may allow access to cookies and other browser data, CSRF vulnerabilities, and access to other resources served on the same domain or parent domains. This is fixed in version 1.27.0.","status":"published","published":"2021-03-26T20:15:00Z","modified":"2023-11-08T04:04:41.638851Z","updated_at":"2026-11-02T15:52:52.682031Z"}]}}