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Synology Safe Access CVE-2025-10466

| EUVDEUVD-2025-209953 MEDIUM
Cross-site Scripting (XSS) (CWE-79)
2026-05-27 security@synology.com GHSA-q5vj-c9px-46jv
5.9
CVSS 3.1 · Vendor: synology
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Obtain or compromise SRM admin credentials
  2. Delivery
    Inject XSS payload into Safe Access configuration
  3. Exploit
    Induce second administrator to load affected SRM page
  4. Execution
    Injected script executes in SRM browser context
  5. Impact
    Read or write non-sensitive SRM files or trigger limited DoS

Vulnerability Assessment

Weakness
CWE
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V1 - Encoding and Sanitization Output encoding, context-aware escaping
MITRE ATT&CK

2 techniques across 2 tactics: Initial Access, Execution

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

Exploitation Conditions

Exploitation requires an active administrator-level authenticated session on the Synology SRM interface (PR:H per CVSS), meaning the attacker must already possess or compromise a full admin account - not a standard user. Additionally, a second user interaction is required (UI:R): another administrator must load or interact with content containing the injected payload. The vulnerability is limited to Synology devices running SRM with the Safe Access package installed and at a version prior to 1.3.1-0329. Limiting factors: administrator privilege prerequisite is a high bar for external attackers; UI:R prevents fully autonomous exploitation; impact is restricted to non-sensitive file read/write and limited DoS within SRM, ruling out credential theft or remote code execution. Default SRM deployments with a single administrator account reduce the realistic multi-admin interaction surface significantly.

Impact

The composite risk picture here is low. CVSS 5.9 Medium reflects the Scope:Changed escalation and network vector, but is significantly constrained by the PR:H requirement - only existing administrator accounts can trigger this vulnerability. User interaction (UI:R) adds a further barrier, meaning a second administrator would need to load attacker-crafted content. EPSS at 0.03% (11th percentile) confirms this is well below typical exploitation thresholds, and SSVC signals no automated exploitation path (Automatable: no) and only partial technical impact. CISA KEV does not list this CVE, and no public proof-of-concept has been reported. The described impact - reading or writing non-sensitive files and limited DoS within SRM - is narrow even if exploitation succeeds. Overall this is a low-priority patching item for most organizations: real-world harm requires a compromised or rogue admin account targeting another admin, not an external attacker against default configurations.

Exploit ScenarioDerived

An authenticated administrator on a vulnerable SRM deployment injects a malicious script payload into a Safe Access configuration field that is later rendered in the SRM interface for another administrator. When the second admin loads the affected page (UI:R), the injected script executes in the SRM web context and can read or write specific non-sensitive files accessible to the SRM application, or trigger limited service disruption. No public proof-of-concept exists at time of analysis, and successful exploitation requires control of an administrator account plus a second-admin interaction vector.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – May 27, 2026

Stored XSS in Synology Safe Access before 1.3.1-0329 on SRM (Synology Router Manager) allows remote authenticated administrators to inject malicious scripts that execute in the SRM context, enabling limited reads or writes of non-sensitive files and constrained denial-of-service conditions. The CVSS Scope:Changed rating confirms cross-component impact - the vulnerability originates in the Safe Access module but affects the broader SRM platform. No public exploit code exists and no active exploitation has been identified; EPSS at 0.03% and SSVC exploitation status of 'none' collectively indicate negligible current threat in the wild.

RemediationAI

Upgrade Synology Safe Access to version 1.3.1-0329 or later, as confirmed by Synology advisory SA_25_11 at https://www.synology.com/en-global/security/advisory/Synology_SA_25_11. This is the primary and recommended fix; vendor-released patched version 1.3.1-0329 is confirmed available. As an interim compensating control, organizations may restrict Safe Access administrative access to trusted internal networks only, reducing the network-reachable attacker surface - this does not eliminate the vulnerability but raises the bar for exploitation since the CVSS attack vector is Network. Given that the vulnerability requires administrator-level credentials and user interaction, enforcing multi-admin environments with strong authentication (e.g., 2FA on SRM admin accounts) further limits realistic exploitability while patching is scheduled.

Affected VersionsENISA

Safe Access * <1.3.1-0329

Affected Packages

euvd safe_access fix: 1.3.1-0329

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

Synology Safe Access is a parental-control and web-filtering application running within Synology Router Manager (SRM), the OS layer of Synology-branded routers. CWE-79 (Improper Neutralization of Input During Web Page Generation) indicates that user-supplied input is reflected or stored and subsequently rendered without adequate sanitization or encoding, allowing script injection into the SRM web interface. The CVSS vector AV:N/AC:L/PR:H/UI:R/S:C captures the core mechanics: the attack is network-delivered, requires no special conditions to set up (AC:L), demands administrator credentials (PR:H), requires a victim to interact with the malicious content (UI:R), and the exploit scope extends beyond the Safe Access component into SRM (S:C). Affected versions are all Safe Access releases prior to 1.3.1-0329 per EUVD-2025-209953 and Synology advisory SA_25_11.

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Severity by source

Vendor (synology) PRIMARY 5.9 MEDIUM
AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L

Primary rating from Vendor (synology) · only source for this CVE.

CVSS VectorVendor: synology

Attack Vector
Network
Attack Complexity
Low
Privileges Required
High
User Interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
Low

Lifecycle Timeline

1
Patch available
May 27, 2026 - 19:46 EUVD

DescriptionCVE.org

Improper neutralization of input during web page generation ('Cross-site Scripting') vulnerability in Safe Access in Synology Safe Access before 1.3.1-0329 allows remote authenticated users with administrator privileges to read or write specific files containing non-sensitive information or conduct limited denial-of-service in SRM.

Threat Intelligence Overview

EPSS Score
0.0%
Top 89% exploitable
Data Quality
6 sources
Confidence: High

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
No
Human Impact· derived
Medium
Technical Impact
Partial

Priority Score

30
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +30
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Cross-Site Scripting occurs when an application accepts untrusted data and sends it to a web browser without proper validation or encoding.

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