What is CVE-2018-12423?

CVE-2018-12423 is a high-severity vulnerability in Matrix Synapse. CVSS score: 7.5/10. Published 2018-06-14.

How severe is CVE-2018-12423?

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

Vulnerability in Matrix Synapse

CVE-2018-12423

In Synapse before 0.31.2, unauthorised users can hijack rooms when there is no m.room.power_levels event in force.

Published 2018-06-14 · 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:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.018 (78.1th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 78th percentile — 78.1% 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

matrix.org/blog/2018/06/14/security-update-synapse-0-31-2/ (Vendor Advisory)
github.com/matrix-org/matrix-doc/issues/1304 (Third Party Advisory)
bugs.debian.org/901549 (Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2018-12423?: CVE-2018-12423 is a high-severity vulnerability in Matrix Synapse. CVSS score: 7.5/10. Published 2018-06-14.
How severe is CVE-2018-12423?: High severity. CVSS v3 base score is 7.5 out of 10.