Security readout for executives and security teams
Plain-English summary
This flaw affects Synology DSM before 6.2.3-25426-3. A network man-in-the-middle attacker could abuse inbound QuickConnect traffic to run arbitrary commands, creating risk to stored data and device control.
Executive priority
Treat as high priority for NAS or storage environments using Synology QuickConnect. Prioritize internet-adjacent or remote-access devices because compromise could affect confidentiality, integrity, and availability of stored business data.
Technical view
CVE-2021-26566 is a CWE-201 issue in DSM synorelayd involving sensitive information inserted into sent data. The CVSS 3.1 score is 8.3 with network attack vector, high complexity, no privileges, user interaction required, changed scope, and high CIA impact.
Likely exposure
Exposure is most relevant to Synology DSM systems older than 6.2.3-25426-3 that use inbound QuickConnect traffic. The provided sources do not enumerate specific models or all affected builds.
Exploitation context
The CVE describes man-in-the-middle attackers executing arbitrary commands through inbound QuickConnect traffic. CISA KEV status is false in the supplied bundle, and no cited source here confirms active exploitation.
Researcher notes
The source bundle supports arbitrary command execution via MITM against inbound QuickConnect traffic, but does not include exploit maturity, affected model list, or detailed remediation beyond the DSM fixed-version boundary.
Mitigation direction
- Update DSM according to Synology advisory SA-20-26.
- Ensure DSM is not running a version before 6.2.3-25426-3.
- Review whether QuickConnect exposure is required for each device.
- Check Synology guidance for supported fixed releases and upgrade paths.
Validation and detection
- Inventory Synology DSM devices and record DSM versions.
- Identify any DSM version earlier than 6.2.3-25426-3.
- Confirm whether QuickConnect is enabled and used for inbound access.
- Review logs for unexpected administrative actions or command execution indicators.
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-201: 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 lookupCVE-2021-26566 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
- High
- CVSS
- 8.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/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:H/PR:N/UI:R/S:C/C:H/I:H/A:H1.66Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.3HighVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://www.synology.com/security/advisory/Synology_SA_20_26CVE reference · x_refsource_CONFIRM
- https://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1160CVE reference · x_refsource_MISC
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.
Insertion of Sensitive Information Into Sent Data
Insertion of Sensitive Information Into Sent Data represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.