Any registered Signal user can unpin a message in any group on the recipient's device, corrupt that group's pin record, or cast a vote in a poll in a group they are not a member of.

Any registered Signal user can unpin a message in any group on the recipient's device, corrupt that group's pin record, or cast a vote in a poll in a group they are not a member of.

A vulnerability in Signal-iOS versions >= v6.28 allows removed group members to bypass edit-message thread-scoping restrictions, enabling them to modify previously sent group messages.