CVE-2025-13476: 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 T

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CRITICAL 9.8REMOTEUPGRADEDOWNGRADE

CVE-2025-13476 is a critical-severity flaw (CVSS 9.8) affecting viber, viber. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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)

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 70%)
CISA exploited list	No
Weakness	CWE-327
Published	2026-03-05
Last modified	2026-06-17

Publisher (CNA): CERT/CC · Vendor: rakuten

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-05 19:15 UTCPublished CVE record published
2026-06-17 08:34 UTCUpdated Record last modified

rakuten viber UPGRADE

Affected: >= 25.6.0 and <= 25.8.1.0

Fixed in: newer than 25.8.1.0

Safe to downgrade to: a release before 25.6.0

1. Check installed version

apt-cache policy viber || rpm -q viber || viber --version

2. UPGRADE to newer than 25.8.1.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade viber

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade viber

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 25.6.0 (Debian / Ubuntu)

apt-cache madison viber sudo apt install viber=<VERSION_BEFORE_25.6.0> sudo apt-mark hold viber

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list viber sudo dnf downgrade viber-<VERSION_BEFORE_25.6.0> sudo dnf versionlock add viber

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

rakuten viber DOWNGRADE

Affected: 9.3.0.6 25.7.2.0g

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.3.0.6

1. Check installed version

apt-cache policy viber || rpm -q viber || viber --version

2. No fixed release: DOWNGRADE to a release before 9.3.0.6 (Debian / Ubuntu)

apt-cache madison viber sudo apt install viber=<VERSION_BEFORE_9.3.0.6> sudo apt-mark hold viber

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list viber sudo dnf downgrade viber-<VERSION_BEFORE_9.3.0.6> sudo dnf versionlock add viber

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-13476?

viber: upgrade to newer than 25.8.1.0; viber: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-13476 being exploited?

CVE-2025-13476 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-13476 affect?

CVE-2025-13476 affects viber, viber. Severity is critical (CVSS 9.8). 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 bl

How urgent is CVE-2025-13476?

Priority 47/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

Windows vulnerabilities · Android vulnerabilities

Related CVEs

CVE-2025-55996 MEDIUM 6.3 UPGRADE Viber Desktop 25.6.0 is vulnerable to HTML Injection via the text parameter of the message compose/forward int

References

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