Security readout for executives and security teams
Plain-English summary
This flaw affects Synology DSM before 6.2.3-25426-3. Sensitive communication in synorelayd could occur over cleartext, letting a man-in-the-middle attacker spoof servers through an HTTP session. Business risk is highest where DSM systems are older and users connect over untrusted or interceptable networks.
Executive priority
Prioritize remediation for internet-accessible or remotely used Synology DSM systems, especially those accessed across networks the organization does not control. The issue is high severity but requires attacker positioning and user interaction, which moderates immediate business urgency.
Technical view
CVE-2021-26564 is a CWE-319 cleartext transmission issue in Synology DSM synorelayd. The CVSS 3.1 score is 8.3 with network attack vector, high complexity, no privileges required, user interaction required, changed scope, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is likely limited to Synology DSM installations running versions before 6.2.3-25426-3. The source bundle does not identify other affected Synology products or specific configurations beyond DSM and synorelayd.
Exploitation context
The described attacker is positioned for man-in-the-middle interception and can spoof servers via an HTTP session. The bundle does not provide evidence of active exploitation, and KEV status is false, so treat exploitation-in-the-wild as unconfirmed.
Researcher notes
Evidence supports DSM before 6.2.3-25426-3 as affected. Do not assume broader Synology product exposure from this bundle. Validation should focus on version confirmation, advisory mapping, and whether affected DSM systems expose the vulnerable synorelayd behavior.
Mitigation direction
- Upgrade Synology DSM to 6.2.3-25426-3 or later.
- Review Synology advisory Synology_SA_20_26 for product-specific update guidance.
- Reduce use of untrusted networks for DSM access until updated.
- Monitor Synology advisories for any additional affected-version clarification.
Validation and detection
- Inventory Synology DSM systems and record installed DSM versions.
- Flag any DSM version earlier than 6.2.3-25426-3.
- Confirm whether synorelayd is present or relevant on affected systems.
- Document update status and remaining exceptions for vulnerability management.
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-319: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. 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-2021-26564 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.
Cleartext Transmission of Sensitive Information
Cleartext Transmission of Sensitive Information represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.