CVE-2023-42453Network attack vector

Forged read receipts via missing authorization checks

Published Sep 26, 2023 · Updated Jun 18, 2025

Improper authorization in Matrix.org Synapse before 1.93.0 allows remote authenticated users to forge read receipts for inaccessible events. The receipt handlers accepted client receipts without verifying that the requester could view the referenced event and remote receipts without confirming that the origin server belonged to the room. A valid account plus known room and event identifiers is sufficient; the flaw changes displayed read state but does not reveal event content.

CVSS severity4.3
Medium
EPSS probability0.65%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authorization in Matrix.org Synapse before 1.93.0 allows remote authenticated users to forge read receipts for inaccessible events. The receipt handlers accepted client receipts without verifying that the requester could view the referenced event and remote receipts without confirming that the origin server belonged to the room. A valid account plus known room and event identifiers is sufficient; the flaw changes displayed read state but does not reveal event content.

The record

CVE
CVE-2023-42453
Published
Sep 26, 2023
Updated
Jun 18, 2025
Vendor
Matrix.org
Product
Synapse
Classifications
CWE-285, T1565.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 26, 2023CVE publishedPublication date reported by the CVE source.
  2. Jun 18, 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=>= 0.34.0, < 1.93.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Matrix.org · Synapseversion=>= 0.34.0, < 1.93.0

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N

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.

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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-285Improper Authorization
T1565.001Stored Data Manipulation

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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