CVE-2020-26891
MEDIUMMatrix Synapse < 1.21.0 - Cross-Site Scripting via Session Parameter in AuthRestServlet
Title source: llmDescription
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.
References (4)
Core 4
Core References
Issue Tracking, Patch, Third Party Advisory x_refsource_misc
https://github.com/matrix-org/synapse/pull/8444
Release Notes, Vendor Advisory x_refsource_misc
https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory
Release Notes, Third Party Advisory x_refsource_misc
https://github.com/matrix-org/synapse/releases/tag/v1.21.2
Patch, Third Party Advisory x_refsource_confirm
https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq
Scores
CVSS v3
6.1
EPSS
0.0193
EPSS Percentile
77.9%
Attack Vector
NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Details
CWE
CWE-79
Status
published
Products (2)
matrix/synapse
< 1.21.0
pypi/matrix-synapse
0 - 1.21.0PyPI
Published
Oct 19, 2020
Tracked Since
Feb 18, 2026