---
title: "NET-TLS-005 TLS Certificate Public Key Too Small"
canonical: https://openvapt.com/checks/NET-TLS-005.html
html: https://openvapt.com/checks/NET-TLS-005.html
site: OpenVAPT, https://openvapt.com/
license: OpenVAPT Source-Available Licence 1.3, https://openvapt.com/legal/licence-text.html
modified: 2026-10-14
version: 0.1.0-alpha.6
---

# NET-TLS-005 TLS Certificate Public Key Too Small

A TLS leaf certificate uses RSA below 2048 bits or an elliptic curve below 256 bits.

- Domain: Network
- Severity: Medium
- Control category: Cryptography and TLS
- Fix effort: medium
- CVSS v3.1 vector: `CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N`
- CIS Controls v8: 3.10
- NIST CSF 2.0: PR.DS-02
- CWE: CWE-326
- OWASP Top 10 2021: A02:2021
- OWASP WSTG v4.2: WSTG-CRYP-01
- NIST SP 800-53 Rev. 5: SC-12, SC-13

## Why It Matters

Undersized public keys provide inadequate security strength and may permit certificate impersonation as cryptanalytic capability improves.

## How It Detects

Reads the leaf public key from loopback TLS handshakes and measures RSA modulus or elliptic curve size.

## How to Fix

Replace the certificate and private key with RSA 2048 bits or stronger, or an approved EC key of at least 256 bits.

## How to Verify

```
Inspect the renewed leaf certificate key size on ports 443, 465, 993, 995, 8443, and 10000. STARTTLS is out of scope.
```

## Learn the Theory

- [P4 TLS, Certificates and HTTPS](https://openvapt.com/academy/p4.md)

## References

- [NIST SP 800-131A Rev. 2, Transitioning the Use of Cryptographic Algorithms and Key Lengths](https://csrc.nist.gov/pubs/sp/800/131/a/r2/final)

## Source Code

https://github.com/OpenVAPT/openvapt/blob/574f7f3333c44b75a3c649e2d93a76d507f75adf/internal/checks/network/tls_depth.go

Run it: `openvapt scan --only NET-TLS-005`. Read it offline: `openvapt explain NET-TLS-005`.

---

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