CVE-2025-30355High· 7.1▾ TwilightSynapse vulnerable to federation denial of service via malformed events
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 39.1 · likelihood 0.2 · exploitation 0
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Exploit-prediction probability, daily snapshots since Jul 8.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via OSV
Last analysed / modified upstream
1.2%
1.2% → 1.2%
A malicious server can craft events with a depth outside the integer range allowed by Canonical JSON. When such an event is received by Synapse version up to 1.127.0, it prevents it from federating with other servers. The vulnerability has been exploited in the wild.
Fixed in Synapse v1.127.1.
Closed federation environments of trusted servers or non-federating installations are not affected.
If you have any questions or comments about this advisory, please email us at security at element.io.
matrix-synapse < 1.127.1Upgrade to a patched release:
matrix-synapse 1.127.1Connected by shared product, vendor, weakness, or advisory.
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