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CVE-2021-26566

27
FAUCET Score

CVE-2021-26566 is a critical vulnerability affecting Synology DiskStation Manager (DSM) versions before 6.2.3-25426-3, as well as other Synology products. It involves the insertion of sensitive information into sent data within the synorelayd service, allowing man-in-the-middle (MITM) attackers to execute arbitrary commands via inbound QuickConnect traffic. With a CVSS score of 9.0 (CRITICAL), this vulnerability has a network attack vector, high attack complexity, and can lead to complete compromise of confidentiality, integrity, and availability. While there is no evidence of active exploitation, public exploit code, or significant community discussion, the potential impact remains severe.

Impacted Technologies

VendorProductVersion(s)CPE
< 6.2.3-25426-3CPE matchmatch criteria
cpe:2.3:o:synology:diskstation_manager:*:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:o:synology:vs960hd_firmware:-:*:*:*:*:*:*:*
Range not provided by sourceCPE matchmatch criteria
cpe:2.3:o:synology:skynas_firmware:-:*:*:*:*:*:*:*
3.0CPE matchmatch criteria
cpe:2.3:o:synology:diskstation_manager_unified_controller:3.0:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

8.3HIGH

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
1.6
Impact Score
6.0
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.49%
Probability of exploitation in next 30 days
EPSS Percentile
71.5%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0149 is in the 65th percentile among its peer group of 201 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.4 Reddit, 1.2 Bluesky, 0.8 Mastodon, and 2.3 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.8 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

synology.com / security/advisory/Synology_SA_20_26
Vendor Advisory
talosintelligence.com / vulnerability_reports/TALOS-2020-1160
ExploitThird Party Advisory