element-hq/synapse · Security
Synapse CPU starvation (Denial of Service)
- GHSA ID
- GHSA-8q93-326v-3m7g
- CVE ID
- CVE-2026-45078
- Severity
- high
- Published
- Updated
- CVSS
- 5.5 · CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CVSS v3
- 5.5 · CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CVSS v4
- 7.1 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Description
Impact
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.
Homeservers that trust all their local users are not at risk.
Patches
Update to Synapse 1.152.1 or later.
Workarounds
If Synapse is deployed behind a reverse proxy, the reverse proxy could be configured to limit the rate of user requests, preventing or increasing the difficulty of the attack.
Identifiers
- ELEMENTSEC-2026-1706
For more information
If you have any questions or comments about this advisory, please email us at security at element.io.
CWEs
- CWE-400 · Uncontrolled Resource Consumption
- CWE-770 · Allocation of Resources Without Limits or Throttling
References
- https://github.com/element-hq/synapse/security/advisories/GHSA-8q93-326v-3m7g ↗
- https://github.com/element-hq/synapse/issues/19394 ↗
- https://github.com/element-hq/synapse/commit/3f58bc50dfba5768ee43ce48c5e74c25ba0b078a ↗
- https://nvd.nist.gov/vuln/detail/CVE-2026-45078 ↗
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2026-191.yaml ↗
- https://github.com/advisories/GHSA-8q93-326v-3m7g ↗