CVE-2025-2848: Synology Mail Server Auth Bypass Flaw

CVE-2025-2848 is an authentication bypass vulnerability in Synology Mail Server that allows authenticated attackers to modify non-sensitive settings and disable non-critical functions. This article covers technical details, impact assessment, affected versions, and recommended mitigation strategies.

CVE-2025-2848 Overview

CVE-2025-2848 is a missing authorization vulnerability [CWE-862] in Synology Mail Server. The flaw allows remote authenticated attackers to read and write non-sensitive settings and disable some non-critical functions on affected installations. The vulnerability affects Synology Mail Server running on Synology DiskStation Manager (DSM) 7.1 and 7.2 platforms. Synology published details in security advisory Synology_SA_25_05, and the CVE was added to the NVD on December 4, 2025.

Critical Impact
Authenticated remote attackers can modify non-sensitive configuration data and disable non-critical functions in Synology Mail Server, degrading service integrity and availability without requiring elevated privileges.

Affected Products

Synology Mail Server on DiskStation Manager (DSM) 7.1
Synology Mail Server on DiskStation Manager (DSM) 7.2
Synology DiskStation Manager 7.1 and 7.2 (as the underlying platform)

Discovery Timeline

2025-12-04 - CVE-2025-2848 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-2848

Vulnerability Analysis

CVE-2025-2848 is classified under [CWE-862] Missing Authorization. The affected component in Synology Mail Server does not verify that an authenticated user is entitled to perform certain configuration operations. As a result, any user with valid credentials can reach functions intended for higher-privileged roles.

The scope of impact is limited to non-sensitive settings and non-critical functions. Attackers cannot directly read confidential mail data or execute arbitrary code through this flaw. They can, however, alter operational parameters and toggle features that legitimate administrators expect to control exclusively.

The vulnerability is exploitable over the network, requires low attack complexity, and needs low privileges. No user interaction is required.

Root Cause

The root cause is the absence of proper authorization checks on selected management endpoints exposed by Synology Mail Server. Authentication alone is treated as sufficient, without verifying whether the authenticated principal holds the administrative role required for the requested action. This design gap enables horizontal and limited vertical privilege escalation within the application.

Attack Vector

An attacker first obtains valid credentials on the target Synology DSM instance. The attacker then issues crafted requests to the Mail Server management interface to read or modify non-sensitive settings or disable non-critical functions. Because the flaw is reachable over the network, exposure of the DSM web interface increases risk.

No public proof-of-concept exploit is available at the time of publication, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Refer to the Synology Security Advisory SA-25-05 for vendor-provided technical context.

Detection Methods for CVE-2025-2848

Indicators of Compromise

Unexpected changes to Synology Mail Server configuration entries made by non-administrator accounts.
Non-critical Mail Server features disabled or re-enabled outside of scheduled administrative windows.
Authenticated HTTP or HTTPS requests from standard user accounts to Mail Server administrative endpoints.

Detection Strategies

Review Synology DSM audit logs for configuration change events tied to Mail Server, correlating the acting account with its assigned role.
Compare current Mail Server settings against a known-good configuration baseline to identify unauthorized deltas.
Alert on any successful management API calls to Mail Server from accounts that do not belong to the administrators group.

Monitoring Recommendations

Forward DSM and Mail Server logs to a centralized logging platform and retain them for post-incident review.
Monitor authentication events for Mail Server and flag accounts issuing management requests they historically have not used.
Track version and patch state of DSM and Mail Server across the estate to confirm remediation coverage.

How to Mitigate CVE-2025-2848

Immediate Actions Required

Apply the Synology-provided Mail Server update referenced in Synology Security Advisory SA-25-05 as soon as it is available for your DSM version.
Audit Mail Server user accounts and remove or disable accounts that are no longer required.
Review Mail Server configuration against a trusted baseline and revert unauthorized changes.

Patch Information

Synology addresses this vulnerability in fixed versions of Synology Mail Server for DSM 7.1 and DSM 7.2. Consult Synology Security Advisory SA-25-05 for the specific fixed package versions and installation instructions. Update through DSM Package Center or by manually installing the patched package.

Workarounds

Restrict network access to the DSM management interface using firewall rules and trusted IP allow lists.
Enforce strong authentication, including two-factor authentication, to raise the cost of obtaining the low-privilege credentials required for exploitation.
Limit Mail Server user accounts to the minimum privilege required and disable accounts that do not need Mail Server access.

bash

# Configuration example: restrict DSM web access to trusted networks
# (adjust interface and subnet to match your environment)
sudo iptables -A INPUT -p tcp --dport 5001 -s 10.0.0.0/24 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 5001 -j DROP