{"id":"ALPINE-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.","modified":"2026-11-03T06:32:31.249599439Z","published":"2020-10-19T17:15:13.220Z","upstream":["CVE-2020-26891"],"references":[{"type":"ADVISORY","url":"https://security.alpinelinux.org/vuln/CVE-2020-26891"}],"affected":[{"package":{"name":"synapse","ecosystem":"Alpine:v3.13","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.14","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.15","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.16","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.17","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.18","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.19","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.20","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.21","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.22","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.23","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}},{"package":{"name":"synapse","ecosystem":"Alpine:v3.24","purl":"pkg:apk/alpine/synapse?arch=source"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.21.1-r0"}]}],"ecosystem_specific":{},"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/alpine/ALPINE-CVE-2020-26891.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"}]}