CVE-2024-31208Network attack vector

Service interruption via transitive auth-chain link expansion

Published Apr 23, 2024 · Updated Feb 13, 2025

Denial of service in Element HQ Synapse before 1.105.1 allows remote authenticated users to exhaust CPU and database storage via crafted events. The _add_chain_cover_index path records transitive event_auth_chain_links for attacker-shaped authorization graphs instead of traversing links at read time. The attacker must share a federated room with the target; private federations and non-federating servers are unaffected, and impact is limited to service interruption through disk growth and high CPU use.

CVSS severity6.5
Medium
EPSS probability1.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Element HQ Synapse before 1.105.1 allows remote authenticated users to exhaust CPU and database storage via crafted events. The _add_chain_cover_index path records transitive event_auth_chain_links for attacker-shaped authorization graphs instead of traversing links at read time. The attacker must share a federated room with the target; private federations and non-federating servers are unaffected, and impact is limited to service interruption through disk growth and high CPU use.

The record

CVE
CVE-2024-31208
Published
Apr 23, 2024
Updated
Feb 13, 2025
Vendor
Element HQ
Product
Synapse
Classifications
CWE-770, T1499.003
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 23, 2024CVE 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=< 1.105.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Element HQ · Synapseversion=< 1.105.1

Published CVSS scores

6.5GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:L/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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 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
T1499.003Application Exhaustion Flood

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

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Your stack

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