What is CVE-2021-27648?

CVE-2021-27648 is a critical-severity vulnerability in Synology Antivirus Essential, classified under Externally Controlled Reference to a Resource in Another Sphere. CVSS score: 9.0/10. Published 2021-04-28.

How severe is CVE-2021-27648?

Critical severity. CVSS v3 base score is 9.0 out of 10.

Is CVE-2021-27648 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Synology Antivirus Essential

CVE-2021-27648

Externally controlled reference to a resource in another sphere in quarantine functionality in Synology Antivirus Essential before 1.4.8-2801 allows remote authenticated users to obtain privilege via unspecified vectors.

Published 2021-04-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.0 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.028 (86.1th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 86th percentile — 86.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.028 · newest: 0.028 · change: 0.000

Affected products

Synology Antivirus Essential
Synology Antivirus Essential — versions unspecified

Weakness classification (CWE)

CWE-610 — Externally Controlled Reference to a Resource in Another Sphere

Public proof-of-concept exploits

References

www.synology.com/security/advisory/Synology_SA_21_15 (Vendor Advisory)

Frequently asked questions

What is CVE-2021-27648?: CVE-2021-27648 is a critical-severity vulnerability in Synology Antivirus Essential, classified under Externally Controlled Reference to a Resource in Another Sphere. CVSS score: 9.0/10. Published 2021-04-28.
How severe is CVE-2021-27648?: Critical severity. CVSS v3 base score is 9.0 out of 10.
Is CVE-2021-27648 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.