CVE-2020-26891

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.

References

Link	Tags
https://github.com/matrix-org/synapse/pull/8444	issue tracking third party advisory patch
https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory	release notes vendor advisory
https://github.com/matrix-org/synapse/releases/tag/v1.21.2	third party advisory release notes
https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq	third party advisory patch

Frequently Asked Questions

What is the severity of CVE-2020-26891?: CVE-2020-26891 has been scored as a medium severity vulnerability.
How to fix CVE-2020-26891?: To fix CVE-2020-26891, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2020-26891 being actively exploited in the wild?: As for now, there are no information to confirm that CVE-2020-26891 is being actively exploited. According to its EPSS score, there is a ~1% probability that this vulnerability will be exploited by malicious actors in the next 30 days.

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Description

Category

CWE-79 – Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

References

Frequently Asked Questions