CVE-2021-26566

HIGHNVD 8.39.0▲Trending — 3 sources updated this week

8.3

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.

CVSS v3: 8.3
EG Score: 9.0(medium)
EPSS: 67.7%
KEV: Not listed

Published

February 26, 2021

Last Modified

January 14, 2025

References (4)

security@synologyhttps://www.synology.com/security/advisory/Synology_SA_20_26
security@synologyhttps://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1160
af854a3a-2127-422b-91ae-364da2661108https://www.synology.com/security/advisory/Synology_SA_20_26
af854a3a-2127-422b-91ae-364da2661108https://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1160

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 13× in last 7d / 13× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-05-31 22:29 UTCepss_batch
2026-05-31 22:29 UTCepss_batch
2026-05-31 00:15 UTCepss_batch
2026-05-29 13:42 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-27 13:39 UTCepss_batch
2026-05-27 13:39 UTCepss_batch
2026-05-26 20:19 UTCEG score recompute
2026-05-26 20:19 UTCGHSA enrichment
2026-05-26 13:42 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch

Frequently asked(5)

What is CVE-2021-26566?

CVE-2021-26566 is a high vulnerability published on February 26, 2021. 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.

When was CVE-2021-26566 disclosed?

CVE-2021-26566 was first published in the National Vulnerability Database on February 26, 2021, with the most recent update on January 14, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-26566 actively exploited?

CVE-2021-26566 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 67.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

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

CVE-2021-26566 has a CVSS v3 base score of 8.3 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.

How do I remediate CVE-2021-26566?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-26566, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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CVE-2021-26566

📅 Published

🔄 Last Modified

🔗 References (4)

Weakness Classification(2)

Data Freshness Timeline

❓ Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-26566?

🔗 Related CVEs(same CWE)

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Published

Last Modified

References (4)

Frequently asked(5)

Related CVEs(same CWE)