{"action":"Upgrade matrix-synapse to 1.21.0 or later.","affected":[{"fixed":"1.21.0","introduced":"0"}],"component":"matrix-synapse","cve_ids":["CVE-2020-26891"],"ecosystem":"PyPI","epss":0.01923,"exploited":false,"fixed_versions":["1.21.0"],"ghsa_id":"GHSA-3x8c-fmpc-5rmq","id":"tcs_01M5KEWS0PCFMXT89PCZA2638T","modified_at":"2026-07-08T06:30:00.309784796Z","published_at":"2020-10-16T16:56:04Z","references":["https://osv.dev/vulnerability/GHSA-3x8c-fmpc-5rmq","https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq","https://nvd.nist.gov/vuln/detail/CVE-2020-26891","https://github.com/matrix-org/synapse/pull/8444","https://github.com/matrix-org/synapse","https://github.com/matrix-org/synapse/releases","https://github.com/matrix-org/synapse/releases/tag/v1.21.2","https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2020-238.yaml","https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory"],"severity":{"label":"medium","score":6.1},"sources":[{"source":"osv","source_id":"GHSA-3x8c-fmpc-5rmq","url":"https://osv.dev/vulnerability/GHSA-3x8c-fmpc-5rmq"}],"summary":"Cross-site scripting (XSS) vulnerability in the fallback authentication endpoint"}