The on_get_missing_events function in handlers/federation.py in Matrix Synapse before 0.31.1 has a security bug in the getmissingevents federation API where event visibility rules were not applied correctly.
{
"severity": "HIGH",
"github_reviewed": true,
"cwe_ids": [],
"nvd_published_at": "2018-06-13T14:29:00Z",
"github_reviewed_at": "2023-07-21T22:50:51Z"
}