XSS in Matrix Synapse
CVE-2020-26891
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.
Vulnerability class: XSS (Cross-Site Scripting)
EPSS: 0.019 (77.9th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
Affected products
- Matrix Synapse
- N/a — versions n/a
Weakness classification (CWE)
References
- cve@mitre.org (Patch, Third Party Advisory, x_refsource_MISC, Issue Tracking)
- cve@mitre.org (x_refsource_MISC, Release Notes, Vendor Advisory)
- cve@mitre.org (Third Party Advisory, x_refsource_MISC, Release Notes)
- cve@mitre.org (x_refsource_CONFIRM, Patch, Third Party Advisory)
Frequently asked questions
- What is CVE-2020-26891?
- CVE-2020-26891 is a medium-severity vulnerability in Matrix Synapse, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2020-10-19.
- How severe is CVE-2020-26891?
- Medium severity. CVSS v3 base score is 6.1 out of 10.