CVE-2020-26890High· 7.5▾ TwilightDenial of service attack due to invalid JSON
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 41.3 · likelihood 0.6 · 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
3.0%
3.0% → 3.0%
A denial of service attack against Matrix clients can be exploited by sending an event including invalid JSON data to Synapse. Synapse would relay the data to clients which could crash or hang. Impact is long-lasting if the event is made part of the room state.
At a minimum #8106 and #8291 must be applied. #7372 and #8124 include additional checks.
There are no known workarounds.
If an invalid event is accepted by an earlier Synapse it can become part of the room state and will not be fixed by upgrading Synapse. Redacting the invalid event should avoid clients receiving the invalid event.
matrix-synapse < 1.20.0Upgrade to a patched release:
matrix-synapse 1.20.0Connected by shared product, vendor, weakness, or advisory.
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