Summary
Synapse Denial of service due to incorrect application of event authorization rules during state resolution
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
[^1]: See m.federate in the m.room.create definition.
For more information
If you have any questions or comments about this advisory, e-mail us at [email protected].
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 disabled[^1] are not affected.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
CVE-2022-39374 has a CVSS score of 6.5 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.68.0rc1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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See it in your environmentNew to Kodem? Get a demo →Remediation advice
Administrators of homeservers with federation enabled are advised to upgrade to 1.68.0 or higher.
Frequently Asked Questions
- What is CVE-2022-39374? CVE-2022-39374 is a high-severity uncontrolled resource consumption vulnerability in matrix-synapse (pip), affecting versions >= 1.62.0, < 1.68.0rc1. It is fixed in 1.68.0rc1. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- How severe is CVE-2022-39374? CVE-2022-39374 has a CVSS score of 6.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of matrix-synapse are affected by CVE-2022-39374? matrix-synapse (pip) versions >= 1.62.0, < 1.68.0rc1 is affected.
- Is there a fix for CVE-2022-39374? Yes. CVE-2022-39374 is fixed in 1.68.0rc1. Upgrade to this version or later.
- Is CVE-2022-39374 exploitable, and should I be worried? Whether CVE-2022-39374 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2022-39374 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2022-39374? Upgrade
matrix-synapseto 1.68.0rc1 or later.