gomatrixserverlib and Dendrite vulnerable to incorrect parsing of the event default power level in event auth

Impact

The power level parsing within gomatrixserverlib was failing to parse the "events_default" key of the m.room.power_levels event, defaulting the event default power level to zero in all cases.

In rooms where the "events_default" power level had been changed, this could result in events either being incorrectly authorised or rejected by Dendrite servers.

Patches

gomatrixserverlib contains a fix as of commit 723fd49 and Dendrite 0.9.3 has been updated accordingly.

Workarounds

Matrix rooms where the "events_default" power level has not been changed from the default of zero are not vulnerable.

For more information

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