What is the CVSS score of CVE-2025-13476?

CVE-2025-13476 has a CVSS 3.1 base score of 9.8 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.0%.

How to fix or mitigate CVE-2025-13476?

Within 24 hours: Inventory all Rakuten Viber deployments across Android (v25.7.2.0g) and Windows (v25.6.0.0–v25.8.1.0) devices; disable Cloak mode feature organization-wide via Mobile Device Management (MDM) or endpoint management policies and communicate restriction to users. Within 7 days: Conduct audit of any communications relying on Cloak mode for security; evaluate alternative circumvention or privacy tools if needed for business operations. Within 30 days: Monitor Rakuten security advisories for patch release; establish process for rapid deployment once available; consider organizational policy on use of Viber for sensitive communications pending remediation.

Viber CVE-2025-13476

CRITICAL

Use of a Broken or Risky Cryptographic Algorithm (CWE-327)

2026-03-05 cret@cert.org

Windows TLS Android Viber Rakuten

9.8

CVSS 3.1 · NVD

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Vulnerability Assessment

Weakness	CWE CWE-327 OWASP Top 10:2025 A04:2025 - Cryptographic Failures ASVS 5.0 V11 - Cryptography Approved algorithm selection
Impact	CVSS 9.8. Privacy bypass in messaging app.
Exploit ScenarioDerived	Identify Viber Cloak mode users through static TLS fingerprint.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.

No patch listed yet 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

Static TLS fingerprint in Rakuten Viber Cloak mode enables tracking despite privacy mode.

Earlier versions of this analysis (1)

v1 Mar 12, 2026 - 22:06 CVSS 9.8

Static TLS fingerprint in Viber privacy mode.

RemediationAI

Update Viber.

Affects your stack

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Technical ContextAI · show details

CWE-327 predictable TLS ClientHello.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 9.8 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

DescriptionCVE.org

Rakuten Viber Cloak mode in Android v25.7.2.0g and Windows v25.6.0.0-v25.8.1.0 uses a static and predictable TLS ClientHello fingerprint lacking extension diversity, allowing Deep Packet Inspection (DPI) systems to trivially identify and block proxy traffic, undermining censorship circumvention. (CWE-327)

Executive ViewAI

Why It Matters

Rakuten Viber's Cloak mode (privacy/circumvention feature) on Android and Windows devices contains a critical flaw that allows network monitoring systems to identify and block Viber traffic despite users' expectation of anonymity. Organizations with employees in restricted network environments or those relying on Viber for secure communications face exposure of user activity and potential regulatory compliance violations if this feature is actively deployed.

Business Impact: High

Compensating Controls

Disable Cloak mode via MDM/endpoint management policies; restrict Viber installation to devices without requirement for circumvention features; route Viber traffic through organizational VPN infrastructure for visibility and control; monitor network traffic for Viber usage patterns to detect DPI blocking events; evaluate alternative communication platforms with verified security postures; implement network segmentation to limit exposure of Viber traffic on sensitive network segments.

Threat Intelligence Overview

EPSS Score

0.0%

Top 91% exploitable

Data Quality

3 sources

Confidence: Low

NVD

CVE.org

EPSS

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 CRITICAL

CISA KEV No

Public POC No

EPSS 0.0%

Patch available No

Active threat No

Deciding rule

CRITICAL severity

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.