Security readout for executives and security teams
Plain-English summary
Some Synology NAS systems could send sensitive information over unencrypted HTTP in DSM’s synorelayd component. An attacker positioned between the user and service could read or manipulate that session data. This is serious for organizations using affected DSM versions, especially over untrusted networks.
Executive priority
Treat this as a high-priority infrastructure hygiene issue for Synology NAS environments. The flaw is not cited as actively exploited, but NAS systems often hold sensitive business data, making timely patch confirmation important.
Technical view
CVE-2021-26565 is a CWE-319 cleartext transmission issue in synorelayd in Synology DiskStation Manager before 6.2.3-25426-3. 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 limited to Synology DSM deployments running versions before 6.2.3-25426-3. Risk is higher where affected NAS management or relay-related traffic crosses untrusted networks or where users can be intercepted by a man-in-the-middle attacker.
Exploitation context
The provided sources do not report active exploitation, and the CVE is not listed as KEV. Exploitation requires a man-in-the-middle position and user interaction, but successful exploitation could expose sensitive information through an HTTP session.
Researcher notes
Focus validation on DSM build level and whether synorelayd-related sessions could traverse interceptable HTTP paths. Evidence in the bundle supports MITM-sensitive information exposure, not public weaponization or a broader affected product list.
Mitigation direction
- Upgrade affected DSM systems to 6.2.3-25426-3 or later per Synology guidance.
- Review Synology advisory Synology_SA_20_26 for product-specific remediation details.
- Restrict DSM access to trusted networks or VPN until remediation is confirmed.
- Avoid exposing affected DSM services over untrusted networks where interception is plausible.
Validation and detection
- Inventory Synology DSM systems and record exact DSM build numbers.
- Confirm no DSM instance remains below 6.2.3-25426-3.
- Review network paths for DSM access crossing untrusted segments.
- Check change records or vulnerability scanner results for applied Synology fixes.
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-2021-26565 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.