Open Redirect in Matrix Synapse
CVE-2021-21273
Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.25.0, requests to user provided domains were not restricted to external IP addresses when calculating the key validity for third-party invite events and sending push notifications. This could cause Synapse to make requests to internal infrastructure. The type of request was not controlled by the user, although limited modification of request bodies was possible. For the most thorough protection server administrators should remove the deprecated `federation_ip_range_blacklist` from their settings after upgrading to Synapse v1.25.0 which will result in Synapse using the improved default IP address restrictions. See the new `ip_range_blacklist` and `ip_range_whitelist` settings if more specific control is necessary.
Vulnerability class: Open Redirect
EPSS: 0.018 (76.4th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 3.1 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:L/A:N.
Affected products
- Matrix Synapse
- Matrix-org Synapse — versions < 1.25.0
- Fedoraproject Fedora — versions 34
Weakness classification (CWE)
References
- security-advisories@github.com (Third Party Advisory, x_refsource_MISC)
- security-advisories@github.com (x_refsource_CONFIRM, Patch, Third Party Advisory)
- security-advisories@github.com (Patch, Third Party Advisory, x_refsource_MISC)
- security-advisories@github.com (Patch, Third Party Advisory, x_refsource_MISC)
- security-advisories@github.com (x_refsource_FEDORA, vendor-advisory)
Frequently asked questions
- What is CVE-2021-21273?
- CVE-2021-21273 is a low-severity vulnerability in Matrix Synapse, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 3.1/10. Published 2021-02-26.
- How severe is CVE-2021-21273?
- Low severity. CVSS v3 base score is 3.1 out of 10.