Security readout for executives and security teams
Plain-English summary
Synology Download Station had an SSRF flaw that could let a logged-in remote user make the system reach internal network resources. The public record rates it medium severity, mainly because authentication is required and the cited impact is limited information exposure, not system takeover.
Executive priority
Treat as a moderate-priority remediation item. Prioritize internet-accessible or broadly accessible Synology deployments, because authenticated users could potentially use the NAS to reach internal resources.
Technical view
CVE-2021-34811 is CWE-918 SSRF in the task management component of Synology Download Station before 3.8.16-3566. CVSS 3.1 is 5.0: network reachable, low complexity, low privileges, no user interaction, changed scope, low confidentiality impact, no integrity or availability impact.
Likely exposure
Exposure is likely limited to organizations running Synology Download Station versions before 3.8.16-3566, especially where authenticated users can access the package remotely or from less trusted networks.
Exploitation context
The provided sources do not show CISA KEV listing or active exploitation. The attack requires a remote authenticated user. The specific vectors are not described in the source bundle, so operational validation should focus on version and access exposure.
Researcher notes
The public details are sparse: the vulnerable task management component and SSRF class are identified, but vectors are unspecified. Do not assume unauthenticated exploitation, code execution, or active exploitation from the provided evidence.
Mitigation direction
- Upgrade Synology Download Station to 3.8.16-3566 or later.
- Review Synology advisory Synology_SA_21_11 for official remediation guidance.
- Restrict Download Station access to trusted users and networks.
- Remove unnecessary remote access to Synology package interfaces.
Validation and detection
- Inventory Synology systems running Download Station.
- Confirm installed Download Station version is 3.8.16-3566 or later.
- Review who can authenticate to Download Station remotely.
- Check whether Download Station is reachable from untrusted network segments.
- Document any systems pending vendor-supported update.
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-918: Information exposure and cloud metadata lookup
Information exposure and SSRF weaknesses can make discovery, cloud metadata, and credential material review relevant. 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 lookupCloud metadata behavior lookup
The CVE wording references SSRF or metadata access, so cloud discovery and credential material review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-34811 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
- Medium
- CVSS
- 5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N
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:L/I:N/A:N3.11.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5MediumVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:N/A:N
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.
Server-Side Request Forgery (SSRF)
Server-Side Request Forgery (SSRF) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.