Mattermost is an open source collaboration platform from Mattermost, Inc. in the United States. Mattermost suffers from a resource management error vulnerability that stems from an inability to check for the presence of custom emoticons when sending it to a post or to limit the number of custom emoticons allowed to be added to a post, which could be exploited by an attacker to send a large number of non-existing custom emoticons in a post and cause a crash.