CVE-2020-26891

moderate-risk
Published 2020-10-19

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.

Do I need to act?

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0.62% chance of exploitation
EPSS score — low exploit probability
-
Not on CISA KEV list
No confirmed active exploitation reported to CISA
?
Patch status unknown
Check vendor advisories for fix availability and mitigation guidance
6
CVSS 6.1/10 Medium
NETWORK / LOW complexity

Affected Products (1)

Affected Vendors

Matrix

References (8)

Issue Tracking https://github.com/matrix-org/synapse/pull/8444
Release Notes https://github.com/matrix-org/synapse/releases/tag/v1.21.2
Patch https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq
Release Notes https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory
Issue Tracking https://github.com/matrix-org/synapse/pull/8444
Release Notes https://github.com/matrix-org/synapse/releases/tag/v1.21.2
Patch https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq
Release Notes https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory
30
/ 100
moderate-risk
Severity 23/34 · High
Exploitability 2/34 · Minimal
Exposure 5/34 · Minimal