---
title: "NET-TLS-003 Self-Signed or Mismatched TLS Certificate"
canonical: https://openvapt.com/checks/NET-TLS-003.html
html: https://openvapt.com/checks/NET-TLS-003.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-003 Self-Signed or Mismatched TLS Certificate

Checks whether each site presents a self-signed certificate, or one that does not cover its name.

- Domain: Network
- Severity: Medium
- Control category: Cryptography and TLS
- Fix effort: low
- CVSS v3.1 vector: `CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:L/A:N`
- CIS Controls v8: 3.10
- NIST CSF 2.0: PR.DS-02
- CWE: CWE-295, CWE-297
- OWASP Top 10 2021: A02:2021, A07:2021
- OWASP ASVS 4.0.3: 9.2.1
- OWASP WSTG v4.2: WSTG-CRYP-01
- NIST SP 800-53 Rev. 5: SC-17
- Benchmark topic: Certificate trust (topic only, no benchmark text)

## Why It Matters

Browsers reject these certificates, so visitors either leave or learn to ignore warnings, which removes protection against interception.

## How It Detects

Reads the leaf certificate from a loopback handshake per site name. Issuer equal to subject means self-signed; the site name must appear in the certificate's DNS names (wildcards honoured).

## How to Fix

Issue a certificate from a public CA covering every site name, for example with certbot --apache or certbot --nginx -d example.com -d www.example.com.

## How to Verify

```
openssl s_client -connect 127.0.0.1:443 -servername <site> </dev/null | openssl x509 -noout -subject -issuer -ext subjectAltName
```

## Learn the Theory

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

## References

- [RFC 6125, Representation and Verification of Domain-Based Application Service Identity](https://www.rfc-editor.org/rfc/rfc6125.html)
- [NIST SP 800-52 Rev. 2, Guidelines for TLS Implementations](https://csrc.nist.gov/pubs/sp/800/52/r2/final)

## Source Code

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

Run it: `openvapt scan --only NET-TLS-003`. Read it offline: `openvapt explain NET-TLS-003`.

---

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