How severe is CVE-2021-27648?

CVE-2021-27648 has a CVSS 3.x base score of 9.0, rated critical severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-27648 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27648?

CVE-2021-27648 affects Synology Antivirus Essential. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-27648?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-27648 published?

CVE-2021-27648 was published on 2021-04-28 and last updated on 2026-06-17.

CVE-2021-27648

CVE-2021-27648 is a critical-severity vulnerability in Synology Antivirus Essential with a CVSS 3.x base score of 9.0. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-610.

Key facts

Severity: Critical (CVSS 3.x base score 9.0)
CVSS v2: 6.5
EPSS exploit prediction: 3% (85th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-610
Affected product: Synology Antivirus Essential
Published: 2021-04-28
Last modified: 2026-06-17

Description

Externally controlled reference to a resource in another sphere in quarantine functionality in Synology Antivirus Essential before 1.4.8-2801 allows remote authenticated users to obtain privilege via unspecified vectors.

Frequently asked questions

What is CVE-2021-27648?: Externally controlled reference to a resource in another sphere in quarantine functionality in Synology Antivirus Essential before 1.4.8-2801 allows remote authenticated users to obtain privilege via unspecified vectors.
How severe is CVE-2021-27648?: CVE-2021-27648 has a CVSS 3.x base score of 9.0, rated critical severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-27648 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (85th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27648?: CVE-2021-27648 affects Synology Antivirus Essential. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-27648?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-27648 published?: CVE-2021-27648 was published on 2021-04-28 and last updated on 2026-06-17.

References

https://www.synology.com/security/advisory/Synology_SA_21_15

Affected products (1)

cpe:2.3:a:synology:antivirus_essential:*:*:*:*:*:*:*:*

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