CVEvulnerability
CVE-2020-26891
6.1 MEDIUM
Official page ↗
- Status
- Modified
- Published
- 2020-10-19
- Last modified
- 2026-06-17
- Assigner
- [email protected]
- CVSS 3.1 ([email protected])
- 6.1 MEDIUM — CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- CVSS 2.0 ([email protected])
- 4.3 MEDIUM — AV:N/AC:M/Au:N/C:N/I:P/A:N
- Weaknesses
- CWE-79
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.
Affected configurations
• matrix synapse (< 1.21.0)
Related
Weakness · CWE (1)
- CWE-79 Improper Neutralization of Input During Web Page Generation weakness
References
- https://github.com/matrix-org/synapse/pull/8444 Issue Tracking, Patch, Third Party Advisory
- https://github.com/matrix-org/synapse/releases/tag/v1.21.2 Release Notes, Third Party Advisory
- https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq Patch, Third Party Advisory
- https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory Release Notes, Vendor Advisory
- https://github.com/matrix-org/synapse/pull/8444 Issue Tracking, Patch, Third Party Advisory
- https://github.com/matrix-org/synapse/releases/tag/v1.21.2 Release Notes, Third Party Advisory
- https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq Patch, Third Party Advisory
- https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory Release Notes, Vendor Advisory