SEC_ERROR_CA_CERT_INVALID

Enterno.io Editorial Team

By Anatoly Oshmanovsky · Updated Apr 18, 2026

Key idea:

SEC_ERROR_CA_CERT_INVALID — Firefox treats the intermediate/root CA cert as invalid. Causes: expired CA cert, malformed DER encoding, deprecated CA (Symantec 2018), root removed from NSS. Fix: replace chain with a fresh intermediate, or switch CA. Let's Encrypt ISRG Root X1 is 2026-valid with no issues.

Below: causes, fixes, FAQ.

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Common Causes

Intermediate CA expired (Let's Encrypt X3 → X1 migration issues)
Root CA removed from NSS store (Symantec, TurkTrust)
Cert chain malformed — not DER/PEM standard
Self-signed root not imported into Firefox trust
Private CA with wrong CA:TRUE BasicConstraints

Step-by-Step Fix

Reissue the cert — modern intermediate chained automatically
For Let's Encrypt: apache2ctl graceful + manual renew
Chain validator: Enterno SSL / SSLLabs
nginx: ssl_certificate fullchain.pem; (fullchain, not cert alone)
Private CA: BasicConstraints=CA:TRUE + valid pathLenConstraint

Check SSL Certificate →

Related SSL Errors

CertificateExpiry, issuer, domains (SAN)

ChainIntermediate and root CA validation

TLS ProtocolTLS version and cipher suite

VulnerabilitiesHeartbleed, POODLE, weak ciphers

Why teams trust us

TLS 1.3

supported

Full

CA chain check

<2s

result

30/14/7

days-to-expiry alerts

How it works

Enter domain

TLS chain verified

Expiry date & vulnerabilities

What Does the SSL Check Cover?

SSL/TLS is the encryption protocol that protects data between the browser and server. Our tool analyzes the certificate, chain of trust, TLS version, and knownvulnerabilities.

Certificate Details

Issuer, validity period, signature algorithm, covered domains (SAN), and validation type (DV/OV/EV).

Chain of Trust

Full chain verification: from leaf certificate through intermediates to root CA.

TLS Analysis

Protocol version (TLS 1.2/1.3), cipher suites, Perfect Forward Secrecy (PFS) support.

Expiry Alerts

Set up a monitor — get Telegram and email alerts 30/14/7 days before expiration.

DV vs OV vs EV Certificates

DV (Domain Validation)

Confirms domain ownership only
Issued in minutes automatically
Free via Let's Encrypt
Suitable for most websites
Most common certificate type

OV / EV

Organization (OV) or Extended Validation (EV)
Issued in 1-5 business days
Costs $50 to $500/year
For finance, e-commerce, government sites
Increases user trust

Who uses this

DevOps

SSL certificate monitoring

Security

TLS config audit

SEO

HTTPS as ranking factor

E-commerce

customer trust

Common Mistakes

❌

Expired certificateBrowsers block sites with expired SSL. Set up auto-renewal or monitoring.

❌

Incomplete certificate chainWithout intermediate CA, some browsers and bots cannot verify the certificate.

❌

Mixed content on HTTPS siteHTTP resources on an HTTPS page — the browser lock icon disappears, reducing trust.

❌

Using TLS 1.0/1.1Legacy TLS versions have known vulnerabilities. Use TLS 1.2+ or 1.3.

❌

Domain mismatch in certificateThe certificate must cover all site domains, including www and subdomains.

Best Practices

✓

Set up auto-renewalLet's Encrypt + certbot with cron — certificate renews automatically every 60-90 days.

✓

Enable HSTSStrict-Transport-Security header forces browsers to always use HTTPS.

✓

Use TLS 1.3TLS 1.3 is faster (1-RTT handshake) and safer — legacy ciphers removed.

✓

Monitor expiration datesCreate a monitor on Enterno.io — get notified well before expiration.

✓

Verify chain after renewalAfter certificate renewal, confirm that intermediate certificates are installed.

Get more with a free account

SSL certificate monitoring, check history and alerts 30 days before expiry.

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Research

TLS 1.3 Adoption 2026: Growth Pace

Errors

Frequently Asked Questions

ISRG Root X1 in 2026?

Active. 2021 → 2035. Cross-signed the old DST Root (expired 2024), but X1 self-trust in 99% of modern stacks.

nginx fullchain vs cert+chain?

Fullchain includes intermediate. nginx does not fetch intermediate automatically; it ships only the leaf cert → Firefox fails validation.

NSS trust store vs OS?

Firefox uses NSS (separate from OS), ~420 roots. Chrome uses OS trust (Windows/macOS) or the Chrome Root Store.

Private CA setup?

OpenSSL ca.cnf + valid extensions. Import .crt via about:preferences#privacy → View Certificates → Import.