CVSS 3.1
6.1 mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:NCVE-2020-26891
Medium (6.1) in matrix synapse. EPSS 1.9% chance of exploitation in the next 30 days. Fixed in matrix-synapse 1.21.0.
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.
Severity
- EPSS
- 1.9% chance of exploitation in the next 30 days; higher than 79% of CVEs (scores of 2026-10-31)
- CWE
- CWE-79
- Published
- Modified
- Record from
- the NVD, synced
Affected
- matrix:synapse
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-3x8c-fmpc-5rmq | PyPI | matrix-synapse | <1.21.0 | 1.21.0 |
| PYSEC-2020-238 | PyPI | matrix-synapse | <1.21.0 | 1.21.0 |
References
- 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
- https://github.com/matrix-org/synapse/pull/8444