CVE-2023-32323Network attack vector

Federation interruption via unbounded invite state

Published May 26, 2023 · Updated Feb 13, 2025

Improper input validation in Matrix.org Synapse before 1.74.0 allows remote authenticated users to interrupt outbound federation. Synapse accepts an unbounded invite_room_state field when creating an invite, producing an oversized event that makes the receiving homeserver reject the whole event batch. An account able to create the required room state and an invite to a user on another homeserver is required; messages and state from the attacking server then remain unseen by that destination.

CVSS severity5.0
Medium
EPSS probability0.98%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Matrix.org Synapse before 1.74.0 allows remote authenticated users to interrupt outbound federation. Synapse accepts an unbounded invite_room_state field when creating an invite, producing an oversized event that makes the receiving homeserver reject the whole event batch. An account able to create the required room state and an invite to a user on another homeserver is required; messages and state from the attacking server then remain unseen by that destination.

The record

CVE
CVE-2023-32323
Published
May 26, 2023
Updated
Feb 13, 2025
Vendor
Matrix.org
Product
Synapse
Classifications
CWE-20, T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 26, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 13, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.74.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Matrix.org · Synapseversion=< 1.74.0

Published CVSS scores

5.0GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:L
5.3GitHub Advisory DatabaseCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:N/SI:N/SA:L
4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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