What is CVE-2021-26569?

CVE-2021-26569 is a critical-severity vulnerability in Synology Diskstation Manager, classified under Race Condition within a Thread. CVSS score: 9.8/10. Published 2021-03-12.

How severe is CVE-2021-26569?

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

Vulnerability in Synology Diskstation Manager

CVE-2021-26569

Race Condition within a Thread 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.

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: 0.023 (82.6th percentile), scored 2026-10-19.

Low probability of exploitation in the next 30 days, but still tracked. 83rd percentile — 82.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.022 · newest: 0.023 · change: +0.001

Affected products

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

Weakness classification (CWE)

References

www.synology.com/security/advisory/Synology_SA_20_26 (Vendor Advisory)
www.zerodayinitiative.com/advisories/ZDI-21-338/ (VDB Entry, Third Party Advisory)

Frequently asked questions

What is CVE-2021-26569?: CVE-2021-26569 is a critical-severity vulnerability in Synology Diskstation Manager, classified under Race Condition within a Thread. CVSS score: 9.8/10. Published 2021-03-12.
How severe is CVE-2021-26569?: Critical severity. CVSS v3 base score is 9.8 out of 10.