CVE-2020-26891

MediumCVSS 6.1/10Last 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.

Metrics

CVSS 3.1 6.1/10CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Weakness enumeration

CWE-79

Affected software

No affected versions have been published.

Timeline

Published
Oct 19, 2020
Last modified
Jun 17, 2026
NVD status
Modified

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