Unrated

Arbitrary File Read/Write and DoS in Synology MailPlus Server

IdentifiersCVE-2025-15660CWE-338

CVE-2025-15660 is a critical vulnerability in Synology MailPlus Server on DiskStation Manager (DSM). The issue is associated with CWE-338, Use of Cryptographically Weak PRNG, and has been identified as ZDI-CAN-28554. Successful exploitation allows an adjacent attacker to read arbitrary files, write arbitrary files, and trigger denial-of-service conditions, resulting in compromise of data confidentiality and integrity as well as service availability. Publicly available context does not provide the specific vulnerable function or code path.

For your environment

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can give an attacker unauthorized access to arbitrary files for reading and modification, enabling theft of sensitive information, tampering with stored data, and disruption of MailPlus Server availability through denial-of-service conditions. The combined effect is high impact to confidentiality, integrity, and availability.

Mitigation

If you can’t patch tonight, do this now.

No vendor workaround or mitigation has been reported beyond applying the security updates. Where immediate patching is not possible, reducing adjacent-network exposure and restricting access to the affected service may lower exposure, but this is not a substitute for upgrading.

Remediation

Patch, then assume compromise.

Upgrade Synology MailPlus Server to a fixed release. For DSM 7.3, upgrade to MailPlus Server 4.0.1-31663 or later. For DSM 7.2.2 and DSM 7.2.1, upgrade to MailPlus Server 4.0.1-21663 or later.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

SynologyMailplus Serverapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

4 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

4 SOURCESView more in app

cyber security newsNews

Jun 30, 2026

Synology MailPlus Server Vulnerabilities Allow Attackers to Trigger DoS Attacks

A critical Synology MailPlus Server vulnerability that allows adjacent attackers to manipulate files and disrupt services, associated with use of a cryptographically weak PRNG.

synologyNews

Jun 26, 2026

Synology_SA_26_11 | Synology Inc.

A critical Synology MailPlus Server vulnerability that allows adjacent attackers to read or write arbitrary files and cause denial-of-service.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity1