Medium severity · published May 28, 2026
CVE-2026-45078
Synapse CPU starvation (Denial of Service)
5.5
CVSS
0.1%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.1% · higher than 2% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
SY
synapse · element-hq
< 1.152.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-45078
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-45078
Mitigation
https://github.com/element-hq/synapse/security/advisories/GHSA-8q93-326v-3m7g
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