{"id":"CVE-2020-26891","details":"AuthRestServlet in Matrix Synapse before 1.21.0 is vulnerable to XSS due to unsafe interpolation of the session GET parameter. This allows a remote attacker to execute an XSS attack on the domain Synapse is hosted on, by supplying the victim user with a malicious URL to the /_matrix/client/r0/auth/*/fallback/web or /_matrix/client/unstable/auth/*/fallback/web Synapse endpoints.","aliases":["GHSA-3x8c-fmpc-5rmq","PYSEC-2020-238"],"modified":"2026-04-10T04:19:02.097824Z","published":"2020-10-19T17:15:13.220Z","related":["GHSA-3x8c-fmpc-5rmq","openSUSE-SU-2024:11041-1"],"references":[{"type":"ADVISORY","url":"https://github.com/matrix-org/synapse/releases/tag/v1.21.2"},{"type":"ADVISORY","url":"https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory"},{"type":"FIX","url":"https://github.com/matrix-org/synapse/pull/8444"},{"type":"FIX","url":"https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/matrix-org/synapse","events":[{"introduced":"0"},{"fixed":"cd0f65d2c71ce8f6cadfa84a6eb6b882d97e36c0"},{"fixed":"9b8a53c7b9e1a3ca5f46e417b9fa705f8bacb494"}],"database_specific":{"versions":[{"introduced":"0"},{"fixed":"1.21.0"}]}}],"versions":["hhs-1","hhs-2","hhs-3","hhs-5","hhs-6","hhs-7","hhs-8","v0.10.0","v0.10.0-r1","v0.10.0-r2","v0.11.0","v0.11.0-r1","v0.11.0-r2","v0.11.1","v0.12.0","v0.13.1","v0.13.2","v0.13.3","v0.14.0","v0.16.0","v0.16.1","v0.16.1-r1","v0.17.0","v0.17.1","v0.17.2","v0.17.3","v0.18.0","v0.18.1","v0.18.2","v0.18.3","v0.18.4","v0.18.5","v0.2.0","v0.2.1","v0.2.1a","v0.2.2","v0.23.0-rc1","v0.23.0-rc2","v0.25.0-rc1","v0.28.0-rc1","v0.3.0","v0.3.3","v0.3.4","v0.32.0","v0.32.0rc1","v0.32.2","v0.4.1","v0.4.2","v0.5.0","v0.5.1","v0.5.2","v0.5.3","v0.5.3a","v0.5.3b","v0.5.3c","v0.5.4","v0.5.4a","v0.6.0","v0.6.0a","v0.6.0b","v0.6.1","v0.6.1a","v0.6.1b","v0.6.1c","v0.6.1d","v0.6.1e","v0.6.1f","v0.7.0","v0.7.0a","v0.7.0b","v0.7.0c","v0.7.0d","v0.7.0e","v0.7.0f","v0.7.1","v0.7.1-r1","v0.7.1-r2","v0.7.1-r3","v0.7.1-r4","v0.8.0","v0.8.1","v0.8.1-r1","v0.8.1-r2","v0.8.1-r3","v0.8.1-r4","v0.9.0","v0.9.0-r1","v0.9.0-r2","v0.9.0-r3","v0.9.0-r4","v0.9.0-r5","v0.9.1","v0.9.2","v0.9.2-r1","v0.9.2-r2","v0.9.3","v0.99.1rc1","v0.99.2rc1","v0.99.4rc1","v0.99.5.1.dev0","v1.1.0rc1","v1.1.0rc2","v1.10.0rc1","v1.11.0rc1","v1.12.0rc1","v1.14.0rc1","v1.15.0rc1","v1.16.0rc1","v1.17.0rc1","v1.18.0rc1","v1.21.0","v1.21.0rc1","v1.21.0rc2","v1.21.0rc3","v1.21.1","v1.3.0rc1","v1.4.0rc1","v1.5.0rc1","v1.6.0rc1","v1.8.0rc1","v1.9.0.dev1","v1.9.0.dev2","v1.9.0rc1"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2020-26891.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"}]}