CVE-2018-12291: Matrix Synapse

High severity, CVSS 7.5. EPSS: 1.8% chance of exploitation in the next 30 days.

The on_get_missing_events function in handlers/federation.py in Matrix Synapse before 0.31.1 has a security bug in the get_missing_events federation API where event visibility rules were not applied correctly.

Affected products

• Matrix Synapse: before 0.31.1 (fixed in 0.31.1)

Published 2018-06-13. Last modified 2026-06-17.