CVE-2023-45129 | 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.

Published: 2023-10-10 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2023-45129 is rated Low Risk (37.2/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.27%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2023-45129

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-20 0.24% 0.27% +0.02%
2 2026-01-04 0.25% 0.24% -0.01%
3 2025-11-21 — 0.25% —

Full EPSS history (15 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2023-45129

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:H)
They need powerful rights—admin, root, or similar—before this pays off.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.2 3.6 [email protected]
4.9 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:H)
They need powerful rights—admin, root, or similar—before this pays off.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.2 3.6 [email protected]

Weakness enumeration for CVE-2023-45129

GitHub Security Advisory for CVE-2023-45129

GHSA-5chr-wjw5-3gq4 · Severity: medium · Ecosystem: pip — matrix-synapse vulnerable to denial of service due to malicious server ACL events

OS Trackers for CVE-2023-45129

vendor priority summary link
alpine — CVE-2023-45129: 1 source package rows (synapse); 32 state rows across 6 repos (3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 6, open 26. https://security.alpinelinux.org/vuln/CVE-2023-45129
debian not yet assigned CVE-2023-45129 not yet assigned priority: Debian including 1 source packages (matrix-synapse), 2 status rows across 2 suites (forky, sid): resolved 2. https://security-tracker.debian.org/tracker/CVE-2023-45129
gentoo low CVE-2023-45129: 1 GLSA(s) (202401-12), 1 atom(s) (net-im/synapse); latest impact low. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2023-45129
redhat medium — https://access.redhat.com/security/cve/CVE-2023-45129
ubuntu medium CVE-2023-45129 medium priority: Ubuntu including 1 source packages (matrix-synapse), 10 status rows across 10 suites (bionic, focal, jammy, lunar, mantic, noble, oracular, trusty, upstream, xenial): ignored 7, not-affected 2, released 1. https://ubuntu.com/security/CVE-2023-45129

Affected software / configurations for CVE-2023-45129

Vendor Product Version Raw CPE
matrix synapse < 1.94.0 cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*
fedoraproject fedora 37 cpe:2.3:o:fedoraproject:fedora:37:*:*:*:*:*:*:*
fedoraproject fedora 38 cpe:2.3:o:fedoraproject:fedora:38:*:*:*:*:*:*:*

References for CVE-2023-45129

cvelogic Threat Intelligence