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. External References: https://github.com/matrix-org/synapse/pull/8444 https://github.com/matrix-org/synapse/releases/tag/v1.21.2 https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory
Created matrix-synapse tracking bugs for this issue: Affects: fedora-all [bug 1906331]
This CVE Bugzilla entry is for community support informational purposes only as it does not affect a package in a commercially supported Red Hat product. Refer to the dependent bugs for status of those individual community products.