Name: CVE-2020-26891: Improper Neutralization of Input During Web Page Generation
Creator: Rapid7
Published: 2020-10-19T00:00:00.000Z
License: https://www.rapid7.com/legal/website-terms-of-use/
Keywords: CVE, CVE-2020-26891, CWE-79, CVSS 6.1, EPSS 0.01923

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.

CVSS Details

CVSS 3.1 Base Score: 6.1
CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N)

Covered by Rapid7

Product	Vendor Advisory	Solution File	Added	Published
Alpine Linux	—	Upgrade synapse	Aug 22, 2024	Oct 19, 2020
Arch Linux	—	Upgrade to the latest version of Arch Linux	Jul 11, 2025	Oct 19, 2020
Freebsd	—	Upgrade py37-matrix-synapseUpgrade py36-matrix-synapseUpgrade py38-matrix-synapseUpgrade py39-matrix-synapse	Oct 18, 2020	Oct 17, 2020

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CVSS Details

Covered by Rapid7

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