How severe is CVE-2021-34809?

CVE-2021-34809 has a CVSS 3.x base score of 9.9, rated critical severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-34809 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (78th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-34809?

CVE-2021-34809 affects Synology Download Station. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-34809?

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-2021-34809 published?

CVE-2021-34809 was published on 2021-06-18 and last updated on 2026-06-17.

CVE-2021-34809

CVE-2021-34809 is a critical-severity vulnerability in Synology Download Station with a CVSS 3.x base score of 9.9. 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-77.

Key facts

Severity: Critical (CVSS 3.x base score 9.9)
CVSS v2: 6.5
EPSS exploit prediction: 2% (78th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-77
Affected product: Synology Download Station
Published: 2021-06-18
Last modified: 2026-06-17

Description

Improper neutralization of special elements used in a command ('Command Injection') vulnerability in task management component in Synology Download Station before 3.8.16-3566 allows remote authenticated users to execute arbitrary code via unspecified vectors.

Frequently asked questions

What is CVE-2021-34809?: Improper neutralization of special elements used in a command ('Command Injection') vulnerability in task management component in Synology Download Station before 3.8.16-3566 allows remote authenticated users to execute arbitrary code via unspecified vectors.
How severe is CVE-2021-34809?: CVE-2021-34809 has a CVSS 3.x base score of 9.9, rated critical severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-34809 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (78th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-34809?: CVE-2021-34809 affects Synology Download Station. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-34809?: 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-2021-34809 published?: CVE-2021-34809 was published on 2021-06-18 and last updated on 2026-06-17.

References

https://www.synology.com/security/advisory/Synology_SA_21_11

Affected products (1)

cpe:2.3:a:synology:download_station:*:*:*:*:*:*:*:*

More vulnerabilities in Synology Download Station

CVE-2021-34810 — Critical (CVSS 9.9): Improper privilege management vulnerability in cgi component in Synology Download Station before 3.8.16-3566 allows…
CVE-2017-11156 — High (CVSS 7.8): Synology Download Station 3.8.x before 3.8.5-3475 and 3.x before 3.5-2984 uses weak permissions (0777) for…
CVE-2021-33184 — High (CVSS 7.7): Server-Side request forgery (SSRF) vulnerability in task management component in Synology Download Station before…
CVE-2017-11149 — Medium (CVSS 6.5): Server-side request forgery (SSRF) vulnerability in Downloader in Synology Download Station 3.8.x before 3.8.5-3475 and…
CVE-2021-34811 — Medium (CVSS 5.0): Server-Side Request Forgery (SSRF) vulnerability in task management component in Synology Download Station before…
CVE-2015-6913 — Medium (CVSS 4.3): Cross-site scripting (XSS) vulnerability in the "Create download task via URL" feature in Synology Download Station…

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