CVE-2024-31208 | Synapse's V2 state resolution weakness allows DoS from remote room members

Synapse is an open-source Matrix homeserver. A remote Matrix user with malicious intent, sharing a room with Synapse instances before 1.105.1, can dispatch specially crafted events to exploit a weakness in the V2 state resolution algorithm. This can induce high CPU consumption and accumulate excessive data in the database of such instances, resulting in a denial of service. Servers in private federations, or those that do not federate, are not affected. Server administrators should upgrade to 1.105.1 or later. Some workarounds are available. One can ban the malicious users or ACL block servers from the rooms and/or leave the room and purge the room using the admin API.

Published: 2024-04-23 Last update: 2025-08-26 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2024-31208 is rated Moderate Risk (58.2/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 4.19%). EPSS rose +1.10% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

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-2024-31208

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 2026-06-01 3.09% 4.19% +1.10%
2 2026-05-12 2.30% 3.09% +0.79%
3 2026-03-04 — 2.30% —

Full EPSS history (42 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2024-31208

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/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:L)
A normal user session is enough; they don’t have to be admin.
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.
 2.8 3.6 [email protected]

Weakness enumeration for CVE-2024-31208

GitHub Security Advisory for CVE-2024-31208

GHSA-3h7q-rfh9-xm4v · Severity: medium · Ecosystem: pip — Synapse V2 state resolution weakness allows Denial of Service (DoS)

OS Trackers for CVE-2024-31208

vendor priority summary link
alpine — CVE-2024-31208: 1 source package rows (synapse); 34 state rows across 4 repos (3.20-community, 3.21-community, 3.22-community, edge-community); fixed 4, open 30. https://security.alpinelinux.org/vuln/CVE-2024-31208
debian not yet assigned CVE-2024-31208 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-2024-31208
ubuntu medium CVE-2024-31208 medium priority: Ubuntu including 2 source packages (matrix-synapse, synapse), 17 status rows across 10 suites (bionic, focal, jammy, mantic, noble, oracular, plucky, questing, upstream, xenial): ignored 8, needs-triage 7, released 2. https://ubuntu.com/security/CVE-2024-31208

Affected software / configurations for CVE-2024-31208

Vendor Product Version Raw CPE
matrix synapse < 1.105.1 cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*
fedoraproject fedora 38 cpe:2.3:o:fedoraproject:fedora:38:*:*:*:*:*:*:*
fedoraproject fedora 39 cpe:2.3:o:fedoraproject:fedora:39:*:*:*:*:*:*:*
fedoraproject fedora 40 cpe:2.3:o:fedoraproject:fedora:40:*:*:*:*:*:*:*

References for CVE-2024-31208

cvelogic Threat Intelligence