CVE-2021-26564

mediumpriority · track · 35OT risk · elevatedEPSS 0.007 · 52 %ileEUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

0.67% (52nd) EPSS

CVSS 5.8 · medium

Is it mine?

5 products

Check your exposure

Who says so?

3 sources

cnnvd · enisa_euvd · nvd

EPSS · scored 2026-10-27

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.

cvss

Technical severity, 0–10. One row per scoring source.

8.7

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 5.8–8.7

v2.05.8mediumAV:N/AC:M/Au:N/C:P/I:P/A:Nprimary · NVD / NIST USexploitability 8.6 · impact 4.9

v3.18.7highCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:Nprimary · NVD / NIST USexploitability 2.2 · impact 5.8

v3.18.3highCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:Hsecondary · ENISA EU

v3.18.3highCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:Hsecondary · security@synology.comexploitability 1.6 · impact 6

v3.18highCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N/E:Usecondary · CVSS-BT (t0sche)

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-319USprimary

affected products (5)

Products and version ranges known to be affected.

Synology Synology DiskStation Manager (DSM)unspecified → 6.2.3-25426-3enisa_euvdEU
synology diskstation manager< 6.2.3-25426-3nvdUScpe:2.3:o:synology:diskstation_manager:*:*:*:*:*:*:*:*
synology diskstation manager unified controller= 3.0nvdUScpe:2.3:o:synology:diskstation_manager_unified_controller:*:*:*:*:*:*:*:*
synology skynas firmwareall versionsnvdUScpe:2.3:o:synology:skynas_firmware:*:*:*:*:*:*:*:*
synology vs960hd firmwareall versionsnvdUScpe:2.3:o:synology:vs960hd_firmware:*:*:*:*:*:*:*:*

also known as (3)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd nvd NVD CVE.org MITRE

published 2021-02-26modified 2026-06-17

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+1178 more

references (8)

External citations — patches, advisories, analysis.

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