Mattermost fails to use innerText / textContent when setting the channel name in the webapp during autocomplete, allowing an attacker to inject HTML to a victim's page by create a channel name that is valid HTML. No XSS is possible though.
{
"versions": [
{
"introduced": "0"
},
{
"last_affected": "7.8.12"
},
{
"introduced": "8.0.0"
},
{
"last_affected": "8.1.3"
}
]
}