Security readout for executives and security teams
Plain-English summary
Synology Download Station had a critical command-injection flaw before version 3.8.16-3566. A remote user with valid credentials could execute arbitrary code through the task management component, potentially affecting confidentiality, integrity, and availability of the NAS environment.
Executive priority
Treat as urgent for any Synology NAS running Download Station, especially internet-reachable or shared environments. Prioritize upgrade validation and access restriction over investigation of exploit details, which are not provided publicly here.
Technical view
CVE-2021-34809 is CWE-77 command injection in Synology Download Station's task management component. CVSS 3.1 is 9.9, with network attack vector, low complexity, low privileges, no user interaction, changed scope, and high CIA impact. Vectors are unspecified in the public description.
Likely exposure
Exposure is limited to Synology systems running Download Station before 3.8.16-3566. Risk is higher where Download Station is reachable over networks used by untrusted or lightly governed authenticated users.
Exploitation context
The provided sources do not report active exploitation, and the bundle marks KEV as false. The vulnerability remains high urgency because authenticated remote code execution can support takeover, data access, or service disruption.
Researcher notes
Public detail is sparse: the affected component and impact are named, but vectors are unspecified. Validate by version and exposure rather than attempting reproduction. Avoid assuming unauthenticated exploitation; the CVSS vector requires low privileges.
Mitigation direction
- Upgrade Synology Download Station to 3.8.16-3566 or later.
- Review Synology advisory SA-21:11 for package-specific guidance.
- Restrict Download Station access to trusted users and trusted networks.
- Remove or disable unused Download Station accounts and permissions.
Validation and detection
- Inventory Synology devices with Download Station installed.
- Confirm Download Station version is 3.8.16-3566 or later.
- Verify remote access paths require trusted network access and authentication.
- Review recent Download Station account activity for unusual authenticated use.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-77: Command execution behavior lookup
Command injection weaknesses can lead defenders to review execution techniques and command interpreter telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-34809 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.9 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H3.16Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.9CriticalVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://www.synology.com/security/advisory/Synology_SA_21_11CVE reference · x_refsource_CONFIRM
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Neutralization of Special Elements used in a Command ('Command Injection')
Improper Neutralization of Special Elements used in a Command ('Command Injection') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.