AUGUST 4, 2026
Live Feed
Back to database
Case File

CVE-2021-21273

LOW · CVSS 3.1 EPSS 1.81% Public Exploit

Source: NVD + CISA KEV + EPSS (historical backfill) · Published 2021-02-26 · Last synced 2026-08-04

CyberRota Analysis

This is a low severity vulnerability with a CVSS score of 3.1. Public exploit code or proof-of-concept references have been detected in its references.

Public Exploit Signal

A public exploit, PoC, GitHub repository or Metasploit reference was detected for this CVE.

Note: these links are listed for security research and verification purposes only.

CVE
CVE-2021-21273
Severity
LOW
CVSS
3.1
EPSS
1.81%

Original NVD Description

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.

Related CVEs

Other vulnerabilities affecting the same vendor(s)