External risk intelligence

Synology DSM Insufficient Entropy Login Vulnerability Allows Arbitrary File Access

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-13639

Synology DiskStation Manager (DSM) is an operating system for network-attached storage devices that is frequently exposed to the internet to enable remote file access, management, and administrative services, making its login interface a primary internet-facing service by design in many common deployments.

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory details a critical vulnerability in Synology DiskStation Manager's login process, which could allow unauthorized access to read or write files and disrupt services. The technology affected is Synology's network-attached storage operating system, commonly used for data management and remote access. The primary concern at this stage is to confirm whether our specific environment utilizes the affected Synology software.

Flaw in login allows unauthorized file access.
Critical vulnerability impacts remote data management.
Confirm if Synology DSM is in use.

Attack Path

How an attacker could exploit the issue

An attacker can target Synology DiskStation Manager's login process, which is often accessible over the internet. By exploiting a weakness in how the system generates random values during login, an attacker could potentially read or modify any file on the system, or even cause the system to stop working.

Remote, unauthenticated access is required.
Exploits insufficient randomness in login.
Allows arbitrary file access and denial-of-service.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability in Synology DiskStation Manager's login logic could allow remote attackers to read or write arbitrary files, potentially leading to data loss or unauthorized modifications. It could also be used to conduct denial-of-service attacks, making the system unavailable.

Arbitrary file read/write access.
Exploited via network without authentication.
System unavailability and data compromise.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability impacts Synology DiskStation Manager (DSM) and may require action from infrastructure, platform, and network/security teams. The first practical step is to identify all DSM instances, determine their internet exposure and business criticality, and then assign ownership for remediation planning.

Identify DSM instances and exposure.
Confirm critical assets and accountable owners.
Plan remediation based on risk assessment.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Synology DiskStation Manager (DSM)?

Synology DiskStation Manager is the web-based operating system that powers Synology network-attached storage (NAS) devices. It provides a central interface for users to manage files, host media, back up data, and run applications, often serving as a private cloud for homes and businesses.

What does insufficient entropy mean in CVE-2026-13639?

Insufficient entropy, classified as CWE-331, means the system fails to generate enough randomness when creating secure values, such as those used during the login process. Because the generated values are predictable, an attacker can bypass security checks, gaining the ability to read or modify files or crash the system.

How does an attacker trigger this vulnerability?

An attacker triggers this by interacting with the login process over the network. Because the flaw exists within the login logic itself, it does not require a valid user account or previous authentication to initiate. Simply having network access to the login interface is enough for an attacker to attempt exploitation.

Is my Synology device at risk?

Your risk depends on whether your device is accessible via the internet. According to Halo Surface Signal, Synology DSM devices are frequently exposed publicly to enable remote file access. If your management interface can be reached from the open internet, it is a primary target for this vulnerability.

What should I do first to address this?

Your first step is to create a complete inventory of all Synology DSM instances within your environment. Once you have identified them, determine which ones are reachable from the internet and prioritize those for review. Work with your team to verify your current software version against the fixed releases specified by Synology.

References

www.synology.com/en-global/security/advisory/Synology_SA_26_13

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.