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CVE-2023-45129

matrix-synapse vulnerable to denial of service due to malicious server ACL events

4.9 MediumFix available

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
High
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
High

Exploit likelihood

1.39%Up 1.3 points since Oct 11, 2023
90%50%10%1%

What each source reports

CVE List Score used 4.9

matrix-synapse vulnerable to denial of service due to malicious server ACL events

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
CVE-2023-45129
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-770
Updated
2026-11-02
EUVDEUVD-2023-0135 4.9

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
EUVD-2023-0135
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-03
GitHub AdvisoriesGHSA-5chr-wjw5-3gq4 6.9

matrix-synapse vulnerable to denial of service due to malicious server ACL events

Impact

A malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service.

Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected.

Patches

Server administrators are advised to upgrade to Synapse 1.94.0 or later.

Workarounds

Rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
GHSA-5chr-wjw5-3gq4
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-770
Updated
2026-11-02
NVD 4.9

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
CVE-2023-45129
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-770
Updated
2026-11-02
OSVALPINE-CVE-2023-45129 4.9

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
ALPINE-CVE-2023-45129
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-03
OSV 4.9

matrix-synapse vulnerable to denial of service due to malicious server ACL events

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
CVE-2023-45129
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-770
Updated
2026-11-02
Show 5 moreShow less
OSVDEBIAN-CVE-2023-45129 4.9

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
DEBIAN-CVE-2023-45129
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVGHSA-5chr-wjw5-3gq4 6.9

matrix-synapse vulnerable to denial of service due to malicious server ACL events

Impact

A malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service.

Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected.

Patches

Server administrators are advised to upgrade to Synapse 1.94.0 or later.

Workarounds

Rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
GHSA-5chr-wjw5-3gq4
CVSS 4.0
6.9 MediumCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Weakness
CWE-770
Updated
2026-11-02
OSVPYSEC-2023-199 4.9

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
PYSEC-2023-199
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2023-45129 4.9

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. Prior to version 1.94.0, a malicious server ACL event can impact performance temporarily or permanently leading to a persistent denial of service. Homeservers running on a closed federation (which presumably do not need to use server ACLs) are not affected. Server administrators are advised to upgrade to Synapse 1.94.0 or later. As a workaround, rooms with malicious server ACL events can be purged and blocked using the admin API.

Record
UBUNTU-CVE-2023-45129
CVSS 3.1
4.9 MediumCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVopenSUSE-SU-2024:13320-1 No score

matrix-synapse-1.94.0-2.1 on GA media

These are all security issues fixed in the matrix-synapse-1.94.0-2.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:13320-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
matrix-synapse
PyPI
 before 1.94.0
1.94.0
synapse
Alpine:v3.18
 before 1.94.0-r0
1.94.0-r0
synapse
Alpine:v3.19
 before 1.94.0-r0
1.94.0-r0
synapse
Alpine:v3.20
 before 1.94.0-r0
1.94.0-r0
synapse
Alpine:v3.21
 before 1.94.0-r0
1.94.0-r0
synapse
Alpine:v3.22
 before 1.94.0-r0
1.94.0-r0
synapse
Alpine:v3.23
 before 1.94.0-r0
1.94.0-r0
synapse
Alpine:v3.24
 before 1.94.0-r0
1.94.0-r0
matrix-synapse
PyPI
 before 1.94.0, plus listed versions
0.33.50.33.5.10.33.60.33.6rc10.33.7
Show 45 moreShow less
0.33.7rc10.33.7rc20.33.80.33.8rc20.33.90.34.00.34.0.10.34.0rc10.34.0rc20.34.1.10.99.00.99.0rc10.99.0rc20.99.0rc30.99.0rc40.99.10.99.1.10.99.1rc10.99.1rc20.99.20.99.2rc10.99.30.99.3.10.99.3.20.99.3rc10.99.40.99.4rc10.99.50.99.5.10.99.5.20.99.5rc11.0.01.0.0rc11.0.0rc21.0.0rc31.1.01.1.0rc11.1.0rc21.10.01.10.0rc11.10.0rc21.10.0rc31.10.0rc51.10.11.11.0
1.94.0
matrix-synapse
Ubuntu:Pro:18.04:LTS
 All versions, plus listed versions
0.19.2+dfsg-60.24.0+dfsg-10.24.0+dfsg-1ubuntu0.1~esm10.24.0+dfsg-1ubuntu0.1~esm4
 None known
matrix-synapse
Ubuntu:Pro:20.04:LTS
 All versions, plus listed versions
1.3.0-11.4.0-11.5.0-11.5.1-11.6.0-1
Show 12 moreShow less
1.6.1-11.7.0-21.7.1-11.7.2-11.7.3-11.8.0-11.9.0-11.9.1-11.10.0-11.10.0-21.11.0-11.11.0-1ubuntu0.1~esm2
 None known
matrix-synapse
Ubuntu:22.04:LTS
 All versions, plus listed versions
1.39.0-11.47.0-21.47.1-11.48.0-11.49.0-1
Show 6 moreShow less
1.49.2-11.50.1-11.50.2-11.51.0-11.52.0-11.53.0-1
 None known
matrix-synapse
openSUSE:Tumbleweed
 before 1.94.0-2.1
1.94.0-2.1

History

History
RecordedChangedSources
affected, aliases, referencesOSV
affected
aliases, products, publishedEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2023-45129 is a medium vulnerability (CVSS 4.9) in Element-hq Synapse, published October 10, 2023. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.39%, the 72nd percentile. Fixed in matrix-synapse 1.94.0.

References

Show 12 moreShow less
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Left out here: 301 versions. The JSON record has them.

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