# CVE-2026-40539: Synology DiskStation Manager improper certificate validation in Email API

Source: https://junglewise.ai/threats/cve-2026-40539-synology-diskstation-manager-improper-certificate-validation-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-18. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-40539 · Severity: high · CVSS 7.1 · Published 2026-09-18

Synology DiskStation Manager (DSM) is the operating system for Synology NAS storage devices used in enterprises and homes to manage data and backups. A flaw in the Email API's certificate validation allows attackers conducting man-in-the-middle attacks to intercept communications, read or modify files on the NAS, and trigger denial-of-service events. This requires network proximity and user interaction but can bypass encryption protections.

Technologies: [Synology DiskStation Manager](https://junglewise.ai/threats/technologies/diskstation-manager). Vendors: [Synology](https://junglewise.ai/threats/vendors/synology).

## Quick answers

**Is CVE-2026-40539 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-40539 being exploited in the wild.

**How severe is CVE-2026-40539?** High severity, with a CVSS score of 7.1, published 18 September 2026.

**Which products and versions are affected?** Synology DiskStation Manager before 7.2.1-69057-10, 7.2.2-72806-7, and 7.3.2-86009-2.

**Is there a fix for CVE-2026-40539?** A patch was published on 2026-04-15: Fixed in DSM 7.2.1-69057-10, 7.2.2-72806-7, and 7.3.2-86009-2 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-40539 attacked?** It is attacked from the adjacent network, in an operating system.

**Am I affected by CVE-2026-40539?** Check whether you run Synology DiskStation Manager at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

CVE-2026-40539 is an improper certificate validation vulnerability (CWE-295) in the Email API component of Synology DSM. The vulnerability allows man-in-the-middle (MITM) attackers to intercept and manipulate Email API communications due to insufficient certificate validation. Attack preconditions include network adjacency and user interaction (UI:R). Successful exploitation enables attackers to read or write arbitrary files on the affected DSM system and launch denial-of-service attacks. Patches are available: DSM 7.2.1-69057-10, DSM 7.2.2-72806-7, and DSM 7.3.2-86009-2 or later.

## Affected products

- Synology DiskStation Manager before 7.2.1-69057-10, 7.2.2-72806-7, and 7.3.2-86009-2

## Timeline

- 2026-09-18: disclosed: CVE published
- 2026-04-15: advisory: Synology advisory SA_26_06 published
- 2026-04-15: patched: Fixed in DSM 7.2.1-69057-10, 7.2.2-72806-7, and 7.3.2-86009-2

## References

- [https://www.synology.com/en-global/security/advisory/Synology_SA_26_06](https://www.synology.com/en-global/security/advisory/Synology_SA_26_06)

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