What is CVE-2021-27647?

CVE-2021-27647 is a critical-severity vulnerability in Synology Diskstation Manager, classified under Out-of-bounds Read. CVSS score: 9.8/10. Published 2021-03-12.

How severe is CVE-2021-27647?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-27647 known to be exploited?

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

Out-of-bounds Read in Synology Diskstation Manager

CVE-2021-27647

Out-of-bounds Read vulnerability in iscsi_snapshot_comm_core in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows remote attackers to execute arbitrary code via crafted web requests.

Vulnerability class: Buffer Overflow

Published 2021-03-12 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.032 (88.1th percentile), scored 2026-10-19.

Low probability of exploitation in the next 30 days, but still tracked. 88th percentile — 88.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.031 · newest: 0.032 · change: +0.001

Affected products

Synology Diskstation Manager
Synology Diskstation Manager (Dsm) — versions unspecified

Weakness classification (CWE)

CWE-125 — Out-of-bounds Read

Public proof-of-concept exploits

X1ngn/sakura_

References

www.synology.com/security/advisory/Synology_SA_20_26 (Vendor Advisory)
www.zerodayinitiative.com/advisories/ZDI-21-339/ (VDB Entry, Third Party Advisory)

Frequently asked questions

What is CVE-2021-27647?: CVE-2021-27647 is a critical-severity vulnerability in Synology Diskstation Manager, classified under Out-of-bounds Read. CVSS score: 9.8/10. Published 2021-03-12.
How severe is CVE-2021-27647?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-27647 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.