What is CVE-2018-16515?

CVE-2018-16515 is a high-severity vulnerability in Matrix Synapse, classified under Improper Verification of Cryptographic Signature. CVSS score: 8.8/10. Published 2018-09-18.

How severe is CVE-2018-16515?

High severity. CVSS v3 base score is 8.8 out of 10.

Vulnerability in Matrix Synapse

CVE-2018-16515

Matrix Synapse before 0.33.3.1 allows remote attackers to spoof events and possibly have unspecified other impacts by leveraging improper transaction and event signature validation.

Published 2018-09-18 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.015 (73.9th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 74th percentile — 73.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.015 · newest: 0.015 · change: +0.000

Affected products

Matrix Synapse
Debian Linux — versions 8.0

Weakness classification (CWE)

CWE-347 — Improper Verification of Cryptographic Signature

References

github.com/matrix-org/synapse/issues/3796 (Patch, Third Party Advisory)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
matrix.org/blog/2018/09/06/critical-security-update-synapse-0-33-3-1/ (Vendor Advisory)

Frequently asked questions

What is CVE-2018-16515?: CVE-2018-16515 is a high-severity vulnerability in Matrix Synapse, classified under Improper Verification of Cryptographic Signature. CVSS score: 8.8/10. Published 2018-09-18.
How severe is CVE-2018-16515?: High severity. CVSS v3 base score is 8.8 out of 10.