CVE-2026-40539 Security feature bypass in DiskStation Manager (DSM)
Man-in-the-middle attackers can bypass certificate validation in the Email API to read or write arbitrary files and cause denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-40539?
CVE-2026-40539 is a high-severity vulnerability in Synology DiskStation Manager (DSM), published on 18 Sep 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
An improper certificate validation vulnerability in Email API in Synology DiskStation Manager (DSM) before 7.2.1-69057-10, 7.2.2-72806-7 and 7.3.2-86009-2 allows man-in-the-middle attackers to read or write arbitrary files and conduct denial-of-service attacks.
Weakness: CWE-295
Which versions are affected by CVE-2026-40539?
How do I fix CVE-2026-40539?
No fix has been published for CVE-2026-40539 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-40539 being exploited?
There is no known exploitation of CVE-2026-40539 in the wild and no public exploit code.
Sources
Also known as GHSA-mqfj-89cq-4gj9.