CVE-2020-26891 Information

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.

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Reference

https://github.com/matrix-org/synapse/pull/8444 https://github.com/matrix-org/synapse/releases/tag/v1.21.2 https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory

Attack Complexity

LOW

Privileges Required

NONE

User Interaction Required

NONE

Scope

REQUIRED

Confidentiality Impact

CHANGED

Integrity Impact

LOW

Availability Impact

LOW

Base Score

NONE

Base Severity

6.1