CVE-2020-26891
Cross-site scripting (XSS) vulnerability in the fallback authentication endpoint
6.1
MEDIUM
CVSS 3.1
EPSS 0.44%
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.
How to fix CVE-2020-26891
To remediate CVE-2020-26891, upgrade the affected package to a fixed version below.
- —upgrade to 1.21.1-1 or later
- —upgrade to 1.21.0 or later
- —upgrade to 1.21.0 or later
Is CVE-2020-26891 being exploited?
Low — EPSS is 0.4%, meaning exploitation activity has not been observed at scale.
Affected packages (3)
- from 0, < 1.21.1-1
- from 0, < 1.21.0
- from 0, < 1.21.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N |
| osv | CVSS 3.1 | MEDIUM6.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N |