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.

• CWE-601
• CWE-601

• https://github.com/matrix-org/synapse/commit/30fba6210834a4ecd91badf0c8f3eb278b72e746Patch, Third Party Advisory
• https://github.com/matrix-org/synapse/pull/8821Patch, Third Party Advisory
• https://github.com/matrix-org/synapse/releases/tag/v1.25.0Third Party Advisory
• https://github.com/matrix-org/synapse/security/advisories/GHSA-v936-j8gp-9q3pPatch, Third Party Advisory
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/
• https://github.com/matrix-org/synapse/commit/30fba6210834a4ecd91badf0c8f3eb278b72e746Patch, Third Party Advisory
• https://github.com/matrix-org/synapse/pull/8821Patch, Third Party Advisory
• https://github.com/matrix-org/synapse/releases/tag/v1.25.0Third Party Advisory
• https://github.com/matrix-org/synapse/security/advisories/GHSA-v936-j8gp-9q3pPatch, Third Party Advisory
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/

Published

Feb 26, 2021

Last Modified

Jun 17, 2026

Status

Modified

• One Click Account Takeover in GranolaHow a notification link broke out of Electron and led to a one-click account takeover.
• Autonomous PentestingAI agents that find and validate exploitable vulnerabilities like this one across your applications.
• PR ReviewsPentest every pull request so vulnerable code is caught before it ships to production.
• AI Penetration TestingHow AI-driven penetration testing continuously covers your attack surface.

• CVE-2021-21267Schema-Inspector is an open-source tool to sanitize and vali…7.5
• CVE-2021-21269Keymaker is a Mastodon Community Finder based Matrix Communi…6.5
• CVE-2021-2127Vulnerability in the Oracle VM VirtualBox product of Oracle …4.4
• CVE-2021-21270OctopusDSC is a PowerShell module with DSC resources that ca…5.5
• CVE-2021-21271Tendermint Core is an open source Byzantine Fault Tolerant (…6.5
• CVE-2021-21272ORAS is open source software which enables a way to push OCI…7.7
• CVE-2021-21274Synapse is a Matrix reference homeserver written in python (…6.5
• CVE-2021-21275The MediaWiki "Report" extension has a Cross-Site Request Fo…4.3
• CVE-2021-21276Polr is an open source URL shortener. in Polr before version…9.3
• CVE-2021-21277angular-expressions is "angular's nicest part extracted as a…8.8
• CVE-2021-21278RSSHub is an open source, easy to use, and extensible RSS fe…9.8
• CVE-2021-21279Contiki-NG is an open-source, cross-platform operating syste…7.5