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No exploitation reportedFix available

CVE-2021-26566

No exploitation reported by the sources we read.

  • Published2021-02-26
  • Fixed in6.2.3-25426-3
  • WeaknessCWE-200 · CWE-201

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Insertion of sensitive information into sent data vulnerability in synorelayd in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows man-in-the-middle attackers to execute arbitrary commands via inbound QuickConnect traffic.

Timeline

dates in UTC
  1. 2021-02-2622:15CVE publishedNVD

Versions per branch

NVD
Synology diskstation manager
BranchAffectedFixed in
6.2< 6.2.3-25426-36.2.3-25426-3
Synology diskstation manager unified controllerversion to verify
BranchAffectedFixed in
3.0= 3.0no fix published
Synology skynas firmwareversion to verify
BranchAffectedFixed in
—all versionsno fix published

1 more product in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

  1. Update Synology diskstation manager to 6.2.3-25426-3

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • CNACVSS 3.18.3known since 2026-10-23
  • NVDCVSS 3.19read 2026-10-23
  • NVDCVSS 2.06.8read 2026-10-23
  • CNAweakness (CWE)CWE-201known since 2026-10-23
  • NVDweakness (CWE)CWE-200read 2026-10-23
  • FIRST EPSSEPSS score1.5 %2026-11-09
  • GitHub Advisoriesadvisory—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Published
2021-02-26
Last Modified
2026-06-17
NVD status
Modified
GitHub Advisory
GHSA-x5fh-xfvr-gg7m

Frequently asked questions

What is CVE-2021-26566?

Insertion of sensitive information into sent data vulnerability in synorelayd in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows man-in-the-middle attackers to execute arbitrary commands via inbound QuickConnect traffic.

Is CVE-2021-26566 actively exploited?

Active exploitation of CVE-2021-26566 has not been confirmed. Its EPSS score was 1.5% on 2026-11-09, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-26566?

CVE-2021-26566 has a CVSS v3 base score of 9 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H.

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