Security readout for executives and security teams
Plain-English summary
This flaw can let an attacker who can intercept or alter relevant network traffic make a vulnerable Synology NAS run attacker-controlled code. That is business-critical because NAS devices often hold backups, shared files, and operational data. The affected product is Synology DSM before 6.2.3-25426-3.
Executive priority
Prioritize remediation for any vulnerable Synology NAS because successful compromise could affect confidentiality, integrity, and availability of stored business data. Urgency is highest where devices are used for backups, file shares, or sensitive records and traffic may traverse untrusted networks.
Technical view
CVE-2021-26562 is a CWE-787 out-of-bounds write in DSM synoagentregisterd. The CVE states a man-in-the-middle attacker can trigger arbitrary code execution through the syno_finder_site HTTP header. CVSS 3.1 is 9.0 with network attack vector, no privileges, no user interaction, high impact, and high attack complexity.
Likely exposure
Exposure is limited to Synology DiskStation Manager versions before 6.2.3-25426-3. Risk depends on whether an attacker can intercept or manipulate the relevant HTTP traffic. The bundle does not identify specific NAS models or deployment configurations beyond DSM.
Exploitation context
The source bundle says exploitation requires a man-in-the-middle position and enables arbitrary code execution. CISA KEV is false in the supplied data, and no cited source in the bundle confirms active exploitation. Treat exploit status as unconfirmed.
Researcher notes
The key technical facts are an out-of-bounds write in synoagentregisterd, the syno_finder_site HTTP header as the trigger surface, and MITM positioning as the stated attacker context. The bundle does not provide enough evidence to claim internet-wide exploitation or affected model granularity.
Mitigation direction
- Upgrade Synology DSM to 6.2.3-25426-3 or later.
- Review Synology advisory SA-20:26 for product-specific guidance.
- Limit DSM management traffic to trusted networks where possible.
- Reduce exposure to untrusted or interceptable network paths until updated.
Validation and detection
- Inventory Synology DSM devices and record installed DSM versions.
- Flag any DSM version earlier than 6.2.3-25426-3.
- Check whether DSM management or discovery traffic crosses untrusted networks.
- Confirm remediation against Synology SA-20:26 and change records.
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-787: 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 lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-26562 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.
Out-of-bounds Write
Out-of-bounds Write represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.