CVE-2022-39374 is a medium-severity (CVSS 6.5) Uncontrolled Resource Consumption vulnerability in matrix-synapse. A fix is available for matrix-synapse — see the affected versions and patch details below.
Synapse Denial of service due to incorrect application of event authorization rules during state resolution
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 CVE-2022-39374.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2022-39374 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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
If Synapse and a malicious homeserver are both joined to the same room, the malicious homeserver can trick Synapse into accepting previously rejected events into its view of the current state of that room. This can be exploited in a way that causes all further messages and state changes sent in that room from the vulnerable homeserver to be rejected.
Synapse homeservers are affected by this issue if and only if they are joined to rooms which members of untrusted homeservers are joined or invited to.
- Synapse homeservers in rooms available over public federation are affected.
- Synapse homeservers with federation disabled are not affected.
- Synapse homeservers in a closed federation containing only trusted servers are not affected.
- Synapse homeservers which are only joined to rooms with federation disabled1 are not affected.
Patches
Administrators of homeservers with federation enabled are advised to upgrade to 1.68.0 or higher.
Workarounds
- Federation can be disabled by setting
federation_domain_whitelistto an empty list ([]). from the vulnerable homeserver to be rejected. This issue has been patched in version 1.68.0
References
For more information
If you have any questions or comments about this advisory, e-mail us at [email protected].
Footnotes
-
See
m.federatein them.room.createdefinition. ↩
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | matrix-synapse | ≥ 1.62.0&&< 1.68.0rc1 | 1.68.0rc1pip install --upgrade 'matrix-synapse==1.68.0rc1' |
Detection & 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 1.68.0rc1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2022-39374 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2022-39374 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2022-39374. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Frequently Asked Questions
Is CVE-2022-39374 in your dependencies?
O3 Security finds CVE-2022-39374 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.