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)
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.019 (79.2th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 79th percentile — 79.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.019 · newest: 0.019 · change: 0.000
Affected products
Weakness classification (CWE)
References
- github.com/matrix-org/synapse/pull/8444 (Patch, Third Party Advisory, Issue Tracking)
- matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory (Release Notes, Vendor Advisory)
- github.com/matrix-org/synapse/releases/tag/v1.21.2 (Third Party Advisory, Release Notes)
- github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq (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.