Mattermost fails to check if a custom emoji reaction exists when sending it to a post and to limit the amount of custom emojis allowed to be added in a post, allowing an attacker sending a huge amount of non-existent custom emojis in a post to crash the mobile app of a user seeing the post and to crash the server due to overloading when clients attempt to retrive the aforementioned post.
{
"versions": [
{
"introduced": "0"
},
{
"last_affected": "8.1.7"
},
{
"introduced": "9.0.0"
},
{
"last_affected": "9.1.4"
},
{
"introduced": "9.2.0"
},
{
"last_affected": "9.2.3"
}
]
}