CVE-2023-43796Network attack vector

Remote user enumeration via unchecked federation queries

Published Oct 31, 2023 · Updated Feb 13, 2025

Information disclosure in Matrix.org Synapse before 1.95.1 allows remote attackers to enumerate remote users through federation queries. The on_query_user_devices, on_federation_query_client_keys, and on_claim_client_keys handlers accepted nonlocal user IDs and queried cached devices or keys without verifying that the users belonged to the receiving homeserver. Any network-reachable federation peer can trigger the queries; disclosure is limited to cached device details and identities for remote users already known to the homeserver.

CVSS severity5.3
Medium
EPSS probability0.90%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Matrix.org Synapse before 1.95.1 allows remote attackers to enumerate remote users through federation queries. The on_query_user_devices, on_federation_query_client_keys, and on_claim_client_keys handlers accepted nonlocal user IDs and queried cached devices or keys without verifying that the users belonged to the receiving homeserver. Any network-reachable federation peer can trigger the queries; disclosure is limited to cached device details and identities for remote users already known to the homeserver.

The record

CVE
CVE-2023-43796
Published
Oct 31, 2023
Updated
Feb 13, 2025
Vendor
Matrix.org
Product
Synapse
Classifications
T1087
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 31, 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=< 1.95.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Matrix.org · Synapseversion=< 1.95.1

Published CVSS scores

5.3GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1087Account Discovery

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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