CVE-2021-26564

Name: CVE-2021-26564
Creator: NVD / NIST
Published: 2021-02-26T22:15:20.3+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.7/10EPSS 0.60%

Last modified Jun 17, 2026

CVE-2021-26564 is a high-severity vulnerability rated 8.7/10 on the CVSS scale. Cleartext transmission of sensitive information vulnerability in synorelayd in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows man-in-the-middle attackers to spoof servers via an HTTP session.. EPSS estimates a 0.60% chance of exploitation in the next 30 days.

Description

Cleartext transmission of sensitive information vulnerability in synorelayd in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows man-in-the-middle attackers to spoof servers via an HTTP session.

Metrics

CVSS 3.1

8.7/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N

EPSS Probability

0.60%

44.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Synology	Diskstation Manager	< 6.2.3-25426-3
Synology	Vs960hd Firmware	All versions
Synology	Skynas Firmware	All versions
Synology	Diskstation Manager Unified Controller	3.0

References

https://www.synology.com/security/advisory/Synology_SA_20_26Vendor Advisory
https://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1160Exploit, Third Party Advisory
https://www.synology.com/security/advisory/Synology_SA_20_26Vendor Advisory
https://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1160Exploit, Third Party Advisory

Timeline

Published: Feb 26, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-26564?

How severe is CVE-2021-26564?

CVE-2021-26564 has a CVSS score of 8.7/10 (HIGH severity). The EPSS model estimates a 0.60% probability of exploitation in the next 30 days.

How do I fix CVE-2021-26564?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-26564?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST