Security readout for executives and security teams
Plain-English summary
Synology DSM had a critical cleartext communication flaw in synoagentregisterd before version 6.2.3-25426-3. A suitably positioned network attacker could impersonate a server during an HTTP session, risking sensitive data exposure and system compromise. The source bundle does not show active exploitation.
Executive priority
Treat this as a high-priority remediation item for Synology DSM environments, especially where devices are network-exposed or operationally important. The issue is critical by CVSS, but the provided evidence does not show active exploitation.
Technical view
CVE-2021-26560 is a CWE-319 cleartext transmission issue in Synology DSM synoagentregisterd. The CVSS 3.1 score is 9.0 with network attack vector, high complexity, no privileges, no user interaction, changed scope, and high confidentiality, integrity, and availability impact.
Likely exposure
Exposure is likely limited to Synology DiskStation Manager systems running versions before 6.2.3-25426-3. Risk increases where DSM-related traffic crosses untrusted networks or can be intercepted. The provided sources do not identify other affected products or exact deployment prerequisites.
Exploitation context
The described attacker model is man-in-the-middle server spoofing over an HTTP session. KEV is false, and the provided source bundle does not cite real-world exploitation. High attack complexity suggests positioning and traffic interception requirements matter.
Researcher notes
Evidence supports a cleartext HTTP-session weakness in synoagentregisterd enabling server spoofing by a man-in-the-middle attacker. Public details in the bundle are limited; avoid assuming exploit availability, affected subcomponents beyond synoagentregisterd, or mitigations not named by Synology or Talos.
Mitigation direction
- Review Synology advisory Synology_SA_20_26 for official fixed versions and guidance.
- Upgrade affected DSM systems to 6.2.3-25426-3 or later where vendor-supported.
- Restrict DSM management and agent-related traffic to trusted networks.
- Monitor Synology guidance for any product-specific remediation notes.
- Prioritize systems reachable from shared, remote, or untrusted network paths.
Validation and detection
- Inventory Synology DSM assets and record exact DSM versions.
- Flag DSM versions earlier than 6.2.3-25426-3 for remediation review.
- Check whether DSM-related traffic traverses untrusted or interceptable network segments.
- Confirm remediation status against Synology advisory Synology_SA_20_26.
- Document any systems that cannot be upgraded and their compensating controls.
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-2021-26560 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 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/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:H/PR:N/UI:N/S:C/C:H/I:H/A:H2.26Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9CriticalVector: CVSS:3.1/AV:N/AC:H/PR:N/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_20_26CVE reference · x_refsource_CONFIRM
- https://www.talosintelligence.com/vulnerability_reports/TALOS-2020-1159CVE 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.