CVE-2023-45129Network attack vector

Persistent denial of service via repeated ACL evaluation

Published Oct 10, 2023 · Updated Feb 13, 2025

Denial of service in Matrix.org Synapse before 1.94.0 allows remote authenticated users to hang homeservers via malicious server ACL events. Server ACL checks repeatedly parse glob lists and compile regular expressions for federation traffic rather than caching a precompiled evaluator. Exploitation requires authority to introduce a malicious ACL state event in a federated room, and the persisted event can keep service degraded; closed federations are unaffected.

CVSS severity4.9
Medium
EPSS probability1.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in Matrix.org Synapse before 1.94.0 allows remote authenticated users to hang homeservers via malicious server ACL events. Server ACL checks repeatedly parse glob lists and compile regular expressions for federation traffic rather than caching a precompiled evaluator. Exploitation requires authority to introduce a malicious ACL state event in a federated room, and the persisted event can keep service degraded; closed federations are unaffected.

The record

CVE
CVE-2023-45129
Published
Oct 10, 2023
Updated
Feb 13, 2025
Vendor
Matrix.org
Product
Synapse
Classifications
CWE-770, T1499.004
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 10, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=< 1.94.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Matrix.org · Synapseversion=< 1.94.0

Published CVSS scores

4.9NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
4.9GitHubCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H

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

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Endpoint Denial of Service: Application or System Exploitation

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo