Rakuten Viber Cloak - Android: Use of a Broken or Risky Cryptographic Algorithm
CVE-2025-13476 is a critical-severity use of a broken or risky cryptographic algorithm vulnerability in Rakuten Viber Cloak - Android from Rakuten Viber, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 27.2.0.0g as the first without the flaw, so updating Rakuten Viber Cloak - Android to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.37% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Rakuten Viber Cloak - Android to 27.2.0.0g or a later version.
- Update Rakuten Viber Cloak - Windows to v27.3.0.0 or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Rakuten Viber | Rakuten Viber Cloak - Android | 25.7.2.0g up to, but not including, 27.2.0.0g | 27.2.0.0g |
| Rakuten Viber | Rakuten Viber Cloak - Windows | v25.6.0.0 up to, but not including, v27.3.0.0 | v27.3.0.0 |
| Rakuten | Viber | 25.6.0 through 25.8.1.0; 9.3.0.6 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CISA (ADP).
Official description
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)
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use of a Broken or Risky Cryptographic Algorithm
The product uses a broken or risky cryptographic algorithm or protocol.
How developers prevent this class of flaw
- Ensure that the design allows one cryptographic algorithm to be replaced with another in the next generation or version. Where possible, use wrappers to make the interfaces uniform. This will make it easier to upgrade to stronger algorithms. With hardware, design the product at the Intellectual Property (IP) level so that one cryptographic algorithm can be replaced with another in the next generation of the hardware product.
- Carefully manage and protect cryptographic keys (see CWE-320). If the keys can be guessed or stolen, then the strength of the cryptography itself is irrelevant.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Industry-standard implementations will save development time and may be more likely to avoid errors that can occur during implementation of cryptographic algorithms. Consider the ESAPI Encryption feature.
More Use of a Broken or Risky Cryptographic Algorithm vulnerabilities (CWE-327)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Third-party and government advisories
- kb.cert.org/vuls/id/772695Third Party Advisory
Other references
- viber.com/en/download/Product
Recent Use of a Broken or Risky Cryptographic Algorithm vulnerabilities
- 9.1 Critical severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 8.1 High severity
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