CVE-2022-36009: Incorrect Authorization

gomatrixserverlib is a Go library for matrix protocol federation. Dendrite is a Matrix homeserver written in Go, an alternative to Synapse. 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. Power levels are the matrix terminology for user access level. 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. gomatrixserverlib contains a fix as of commit 723fd49 and Dendrite 0.9.3 has been updated accordingly. Matrix rooms where the events_default power level has not been changed from the default of zero are not vulnerable. Users are advised to upgrade. There are no known workarounds for this issue.