CVE-2020-26891 Details
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.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
No SSVC data is available for this CVE.
References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/matrix-org/synapse/pull/8444 | CVE | Issue TrackingPatchThird Party Advisory |
| https://github.com/matrix-org/synapse/releases/tag/v1.21.2 | CVE | Release NotesThird Party Advisory |
| https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq | CVE | PatchThird Party Advisory |
| https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory | CVE | Release NotesVendor Advisory |
| https://github.com/matrix-org/synapse/pull/8444 | [email protected] | Issue TrackingPatchThird Party Advisory |
| https://github.com/matrix-org/synapse/releases/tag/v1.21.2 | [email protected] | Release NotesThird Party Advisory |
| https://github.com/matrix-org/synapse/security/advisories/GHSA-3x8c-fmpc-5rmq | [email protected] | PatchThird Party Advisory |
| https://matrix.org/blog/2020/10/15/synapse-1-21-2-released-and-security-advisory | [email protected] | Release NotesVendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-79 | Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| matrix synapse | < 1.21.0 |
CPE
Remediation
| |
Change History
5 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Nov 21, 2024 | CVE Modified | CVE |
| May 14, 2024 | CVE Modified | [email protected] |
| Oct 26, 2020 | Initial Analysis | [email protected] |
| Oct 20, 2020 | CVE Modified | [email protected] |