CVE-2020-26891: XSS
First published: Mon Oct 19 2020(Updated: )
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.
Credit: cve@mitre.org
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Matrix Synapse | <1.21.0 |
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Reference Links
Frequently Asked Questions
What is CVE-2020-26891?
CVE-2020-26891 is a vulnerability in Matrix Synapse before version 1.21.0 that allows for XSS attacks due to unsafe interpolation of the session GET parameter.
How can an attacker exploit CVE-2020-26891?
An attacker can exploit CVE-2020-26891 by supplying a malicious URL to the /_matrix/client/r0/auth/* endpoint, which can execute an XSS attack on the domain Synapse is hosted on.
What is the severity of CVE-2020-26891?
CVE-2020-26891 has a severity rating of 6.1 (Medium).
How can I fix CVE-2020-26891?
To fix CVE-2020-26891, upgrade Matrix Synapse to version 1.21.0 or later.
Where can I find more information about CVE-2020-26891?
More information about CVE-2020-26891 can be found in the references provided: [GitHub Pull Request](https://github.com/matrix-org/synapse/pull/8444), [GitHub Release](https://github.com/matrix-org/synapse/releases/tag/v1.21.2), [GitHub Security Advisory](https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq)
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