GHSA-grvv-h2f9-7v9c gomatrixserverlib and Dendrite vulnerable to incorrect parsing of the event default power level in event auth

• Go github.com/matrix-org/dendrite: < 0.9.3 → fixed in 0.9.3 • Go github.com/matrix-org/gomatrixserverlib: < 0.0.0-20220815091947-723fd495dde8 → fixed in 0.0.0-20220815091947-723fd495dde8

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 If you have any questions or comments about this advisory, e-mail us at [email protected].