GHSA-8q93-326v-3m7g is a medium-severity (CVSS 5.5) CWE-770 vulnerability in matrix-synapse. A fix is available for matrix-synapse — see the affected versions and patch details below.
Synapse CPU starvation (Denial of Service)
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-8q93-326v-3m7g.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-8q93-326v-3m7g by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 379,842 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
matrix-synapseReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | matrix-synapse | all versions | 1.152.1pip install --upgrade 'matrix-synapse==1.152.1' |
Affected Products
synapseelementDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-synapse, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update matrix-synapse to 1.152.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8q93-326v-3m7g is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is GHSA-8q93-326v-3m7g in your dependencies?
Find it across PyPI, including transitive dependencies.