CVE-2025-13476
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedRakuten 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)
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceRakuten Viber's Cloak mode uses a static and predictable TLS ClientHello fingerprint that lacks extension diversity. This means the TLS handshake (the initial connection setup) always looks the same, allowing Deep Packet Inspection (DPI) systems to trivially identify and block the proxy traffic by recognizing this unique fingerprint pattern.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 25.6.0, <= 25.8.1.0= 9.3.0.6CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed Viber versionOpen Viber, go to Settings > About > Version, or check via your device's app management screen. Compare the version number to the affected ranges: 25.6.0 through 25.8.1.0, or exactly version 9.3.0.6.Affected if The installed version falls within 25.6.0 to 25.8.1.0, or is exactly 9.3.0.6
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Verify if Cloak mode is enabledOpen Viber, navigate to Settings > Privacy & Security > Cloak, or check the app settings for any Cloak-related proxy or privacy feature. Determine whether the feature is turned on.Affected if Cloak mode is currently enabled in the application settings
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Inspect TLS ClientHello fingerprint (optional)Capture network traffic using a packet analyzer (such as Wireshark) during a Viber connection attempt while Cloak is active. Examine the TLS ClientHello message for extension ordering, supported groups, and signature algorithms. Compare against known browser fingerprints.Affected if The ClientHello exhibits a static, repetitive fingerprint pattern lacking diversity in extensions and values compared to standard browser handshakes
A user is affected if they have an affected Viber version (25.6.0-25.8.1.0 or 9.3.0.6) AND have Cloak mode enabled, resulting in a predictable TLS fingerprint that DPI systems can block.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataImplement dynamic TLS ClientHello fingerprint randomization with diverse extensions and values that mimic standard browser TLS handshakes, ensuring each connection appears as a normal browser to DPI systems.
- Consultation4.0 h
- Implementation16.0 h
- Testing8.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $8,960.
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Free · runs locallyCheck whether your project pulls in CVE-2025-13476 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-13476 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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