Security readout for executives and security teams
Plain-English summary
Synology DSM had a path traversal flaw in its webapi component that let an unauthenticated remote attacker write arbitrary files. For organizations using affected NAS devices, the business risk is unauthorized file modification on storage infrastructure, potentially affecting trust in stored data and device integrity.
Executive priority
Treat as high priority for Synology NAS assets because exploitation requires no authentication and can alter files. Patch exposed devices first, then complete fleet validation and access review.
Technical view
CVE-2021-29087 is CWE-22 in Synology DiskStation Manager before 6.2.3-25426-3. The CVSS 3.1 vector is AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N, reflecting remote, unauthenticated arbitrary file write with high integrity impact and no stated confidentiality or availability impact.
Likely exposure
Exposure is likely where Synology DSM systems older than 6.2.3-25426-3 are reachable over a network, especially where DSM management or webapi access is internet-accessible. The source bundle does not identify specific models or configuration prerequisites beyond DSM version.
Exploitation context
The sources state remote attackers can write arbitrary files via unspecified vectors. CISA KEV status is false in the bundle, and no cited source confirms active exploitation. Exploit mechanics are not described, so weaponization detail should not be assumed.
Researcher notes
The public description is sparse: vectors are unspecified, affected versions are summarized, and model-level scope is not provided in the bundle. Analysis should stay anchored to DSM before 6.2.3-25426-3 and arbitrary file write impact.
Mitigation direction
- Upgrade DSM to 6.2.3-25426-3 or a vendor-supported later fixed release.
- Review Synology advisory SA-20-26 for product-specific update guidance.
- Prioritize exposed DSM systems before internal-only systems.
- Limit DSM management access to trusted networks while updates are pending.
Validation and detection
- Inventory Synology DSM assets and record installed DSM versions.
- Flag any DSM version earlier than 6.2.3-25426-3 as affected.
- Verify DSM web management is not broadly internet-exposed.
- Review device file integrity and administrative logs for unexpected changes.
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-22: File access and web shell behavior lookup
File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. 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 lookupFile access behavior lookup
The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-29087 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
- 7.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
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:L/PR:N/UI:N/S:U/C:N/I:H/A:N3.93.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://www.synology.com/security/advisory/Synology_SA_20_26CVE reference · x_refsource_CONFIRM
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.