What is CVE-2018-12291?

CVE-2018-12291 is a high-severity vulnerability in Matrix Synapse. CVSS score: 7.5/10. Published 2018-06-13.

How severe is CVE-2018-12291?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Matrix Synapse

CVE-2018-12291

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.

Published 2018-06-13 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.018 (77.9th percentile), scored 2026-09-28.

Low probability of exploitation in the next 30 days, but still tracked. 78th percentile — 77.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.018 · newest: 0.018 · change: 0.000

Affected products

Matrix Synapse

References

github.com/matrix-org/synapse/releases/tag/v0.31.1 (Third Party Advisory)
github.com/matrix-org/synapse/pull/3371 (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2018-12291?: CVE-2018-12291 is a high-severity vulnerability in Matrix Synapse. CVSS score: 7.5/10. Published 2018-06-13.
How severe is CVE-2018-12291?: High severity. CVSS v3 base score is 7.5 out of 10.