CVE-2021-21392
MEDIUMDescription
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 1.28.0 requests to user provided domains were not restricted to external IP addresses when transitional IPv6 addresses were used. Outbound requests to federation, identity servers, when calculating the key validity for third-party invite events, sending push notifications, and generating URL previews are affected. This could cause Synapse to make requests to internal infrastructure on dual-stack networks. See referenced GitHub security advisory for details and workarounds.
How to fix
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:H/A:N
Exploit Intelligence
Moderate risk: more likely to be exploited than 55% of all known CVEs.
References
Related Vulnerabilities
Other CWE-601 (Open Redirect) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-4123 | High | 7.6 | 98% | - | Fix |
| CVE-2018-11784 | Medium | 4.3 | 94% | - | Fix |
| CVE-2021-22881 | Medium | 6.1 | 87% | - | Fix |
| CVE-2022-45402 | Medium | 6.1 | 82% | - | Fix |
| CVE-2017-1000117 | High | 8.8 | 78% | - | Fix |
| CVE-2019-10098 | Medium | 6.1 | 74% | - | Fix |
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Markdown
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Start freeThis product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.