CVE-2025-13476Network attack vector

Proxy-use disclosure via rigid TLS fingerprint

Published Mar 5, 2026 · Updated Mar 5, 2026

Fingerprinting weakness in Rakuten Viber Messenger and Viber Desktop allows attackers to identify Cloak proxy use through network traffic. In Cloak mode, the TLS handshake emits a rigid ClientHello fingerprint without extension diversity instead of resembling ordinary browser TLS. Exploitation requires network visibility into a user's Cloak-mode handshake; DPI systems can distinguish and block the proxy traffic, while message-content decryption is not reported.

CVSS severity9.8
Critical
EPSS probability0.34%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Fingerprinting weakness in Rakuten Viber Messenger and Viber Desktop allows attackers to identify Cloak proxy use through network traffic. In Cloak mode, the TLS handshake emits a rigid ClientHello fingerprint without extension diversity instead of resembling ordinary browser TLS. Exploitation requires network visibility into a user's Cloak-mode handshake; DPI systems can distinguish and block the proxy traffic, while message-content decryption is not reported.

The record

CVE
CVE-2025-13476
Published
Mar 5, 2026
Updated
Mar 5, 2026
Vendor
Rakuten Viber
Product
Viber Desktop
Classifications
CWE-327, T1040
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 5, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=v25.6.0.0 <v27.3.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Rakuten Viber · Viber Desktopversion=v25.6.0.0 <v27.3.0.0
Rakuten Viber · Rakuten Viber Messengerversion=25.7.2.0g <27.2.0.0g

Published CVSS scores

9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-327Use of a Broken or Risky Cryptographic Algorithm
T1040Network Sniffing

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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