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TI-2020-16078 Aliases CVE-2020-26257GHSA-hxmp-pqch-c8mm

Denial of service attack via incorrect parameters to federation APIs

Priority LOW 33CWE-400Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Denial of service, Cross-site scripting
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-400 and CWE-79.

Summary

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`).

Why it matters now

EPSS 0.02392 84th percentileScored 2026-11-07
Fix Fixed synapse (matrix-org): 1.23.1matrix-synapse (PyPI): 1.23.1

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
matrix-orgsynapsebefore 1.23.11.23.1Patch availableCNA
—matrix-synapse (PyPI)before 1.23.11.23.1Patch availableGHSA-hxmp-pqch-c8mm
  • synapse Vendormatrix-org Affected before 1.23.1 Fixed in 1.23.1 Patch available CNA
  • matrix-synapse (PyPI) Vendor— Affected before 1.23.1 Fixed in 1.23.1 Patch available GHSA-hxmp-pqch-c8mm

CPE configurations NVD · 3

CPEVersionsRoleVendor
cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*before 1.23.1Vulnerablematrix-org
cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:*32VulnerableFedoraproject
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*33VulnerableFedoraproject
  • cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:* Versions before 1.23.1 Vulnerable ·matrix-org
  • cpe:2.3:o:fedoraproject:fedora:32:*:*:*:*:*:*:* Versions 32 Vulnerable ·Fedoraproject
  • cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:* Versions 33 Vulnerable ·Fedoraproject

Remediation

  • Fix · CNA synapse (matrix-org) Fixed in 1.23.1
  • Fix · GHSA-hxmp-pqch-c8mm matrix-synapse (PyPI) Fixed in 1.23.1 Advisory →

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product
  • Red Hat

Timeline

  1. 2026-10-02 Threatist record created from CVE-2020-26257
  2. 2026-10-03 Alias added: GHSA-hxmp-pqch-c8mm

References

Patch 2

Advisory 5

Other 3

  • TI-2023-15617 Synapse Outgoing federation to specific hosts can be disabled by sending malicious invites CVSS 3.1MEDIUM 5.0
  • TI-2024-35327 Synapse allows a a malformed invite to break the invitee's `/sync` CVSS 4.0HIGH 8.7
  • TI-2019-13571 Matrix Synapse before 1.5.0 mishandles signature checking on some federation APIs. CVSS 3.1CRITICAL 9.8
  • TI-2024-36056 Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders CVSS 4.0HIGH 8.2
  • TI-2024-35318 Synapse allows unsupported content types to lead to memory exhaustion CVSS 4.0HIGH 8.2
  • TI-2018-11846 Matrix Synapse before 0.33.3.1 allows remote attackers to spoof events and possibly have… CVSS 3.0HIGH 8.8
See all 39 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences