CVE-2026-45078 Synapse CPU starvation (Denial of Service)
Authenticated users can cause CPU starvation in Synapse, denying service to other users; administrators should upgrade to the fixed version.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-45078?
CVE-2026-45078 is a medium-severity denial of service vulnerability in element-hq synapse, published on 28 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Weakness: CWE-770
Which versions are affected by CVE-2026-45078?
3 open source packages ship an affected version, including matrix-synapse. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
matrix-synapse PyPI | All versions | 1.152.1 |
matrix-synapse PyPI | All versions | 1.152.1 |
matrix-synapse PyPI | All versions | 1.152.1 |
Products include Element Synapse.
How do I fix CVE-2026-45078?
Upgrade matrix-synapse to 1.152.1 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-45078 being exploited?
There is no known exploitation of CVE-2026-45078 in the wild and no public exploit code.
Other vulnerabilities in element-hq synapse
Sources
Also known as GHSA-8q93-326v-3m7g, PYSEC-2026-191, UBUNTU-CVE-2026-45078.