CVE-2020-26891

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CVSS 3.1

6.1 medium

EPSS

2%p79

Published

Oct 19, 2020 (Oct 19, 2020)

Modified

Jun 17, 2026

Description

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.

Vendors: matrix
Products: synapse
Weakness: CWE-79
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

NVD CVE.org GitHub PoCs EPSS (1.9%)

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