VULNERABILITY INTELLIGENCE

CVE-2020-26257

CVSS score6.5 MEDIUM
EPSS probability2.39%
CISA KEVNot currently listed
Published2020-12-09
Last modified2026-06-17
CVSS vectorCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Description

Matrix is an ecosystem for open federated Instant Messaging and VoIP. Synapse is a reference "homeserver" implementation of Matrix. A malicious or poorly-implemented homeserver can inject malformed events into a room by specifying a different room id in the path of a `/send_join`, `/send_leave`, `/invite` or `/exchange_third_party_invite` request. This can lead to a denial of service in which future events will not be correctly sent to other servers over federation. This affects any server which accepts federation requests from untrusted servers. The Matrix Synapse reference implementation before version 1.23.1 the implementation is vulnerable to this injection attack. Issue is fixed in version 1.23.1. As a workaround homeserver administrators could limit access to the federation API to trusted servers (for example via `federation_domain_whitelist`).

Weakness classification

  • CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
  • CWE-400: Uncontrolled Resource Consumption

Primary references