CVE-2020-26891
6.1 · MEDIUMOverview
CVE-2020-26891 is a medium-severity vulnerability affecting matrix synapse. It was published on October 19, 2020 and has a CVSS 3.1 base score of 6.1 (MEDIUM).
This vulnerability has a CVSS 3.1 base score of 6.1, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
Technical 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.
Remediation
Check the references section for vendor advisories and patches from matrix. Update synapse to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
Affected Products
| Vendor | Product | Versions | Status |
|---|---|---|---|
| matrix | synapse | >= 0, < 1.21.0 | Affected |
References
Frequently Asked Questions
What is CVE-2020-26891?
CVE-2020-26891 is a medium-severity vulnerability affecting matrix synapse. It was published on October 19, 2020 and has a CVSS 3.1 base score of 6.1 (MEDIUM).
How severe is CVE-2020-26891?
This vulnerability has a CVSS 3.1 base score of 6.1, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.
How do I fix or remediate CVE-2020-26891?
Check the references section for vendor advisories and patches from matrix. Update synapse to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.
How can CyberStrike help with CVE-2020-26891?
CyberStrike's AI-powered security agents can automatically detect CVE-2020-26891 across your infrastructure using autonomous pentesting, DAST scanning, and HackBrowser. The platform continuously monitors for known vulnerabilities and provides actionable remediation guidance prioritized by real-world exploitability.
How CyberStrike Helps
AI agents map your attack surface to find vulnerabilities like this one.
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