What is CVE-2026-45078?

CVE-2026-45078 is a medium-severity vulnerability in Element Synapse, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 5.5/10. Published 2026-05-28.

How severe is CVE-2026-45078?

Medium severity. CVSS v3 base score is 5.5 out of 10.

Resource exhaustion in Element Synapse

CVE-2026-45078

Synapse is an open source Matrix homeserver implementation. Prior to 1.152.1, local authenticated users can cause Synapse to starve other requests of CPU and lead to other requests failing, causing other users to be denied service. This vulnerability is fixed in 1.152.1.

Published 2026-05-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.001 (2.4th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 2nd percentile — 2.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.001 · newest: 0.001 · change: +0.000

Affected products

Element Synapse
Element-Hq Synapse — versions < 1.152.1

Weakness classification (CWE)

CWE-770 — Allocation of Resources Without Limits or Throttling

References

github.com/element-hq/synapse/security/advisories/GHSA-8q93-326v-3m7g (Mitigation, Vendor Advisory)

Frequently asked questions

What is CVE-2026-45078?: CVE-2026-45078 is a medium-severity vulnerability in Element Synapse, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 5.5/10. Published 2026-05-28.
How severe is CVE-2026-45078?: Medium severity. CVSS v3 base score is 5.5 out of 10.