ERR_SSL_BAD_RECORD_MAC_ALERT — Corrupted TLS Record

Enterno.io Editorial Team

ERR_SSL_BAD_RECORD_MAC_ALERT: Causes & Fix

By Anatoly Oshmanovsky · Updated Apr 17, 2026

Key idea:

ERR_SSL_BAD_RECORD_MAC_ALERT means the client or server received a TLS record with an invalid MAC (Message Authentication Code). The data was corrupted in transit: network glitch, proxy, antivirus doing TLS inspection, or bad RAM. Fix: disable AV TLS inspection, check MTU, update network drivers.

This error blocks HTTPS access. Below: causes, fixes, working config, FAQ.

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Common Causes

Antivirus/firewall with TLS inspection corrupts data
A broken proxy between client and server
Wrong MTU on the path (fragmentation mangles packets)
Faulty RAM on the server (rare, but happens)
Aggressive TCP offload on the NIC mangles packets
Client: outdated OpenSSL with an AES-GCM bug

Step-by-Step Fix

Temporarily disable the antivirus (Kaspersky/Bitdefender) — did the error go away?
Check MTU: ping -M do -s 1472 8.8.8.8; if fragments — lower to 1400
On the server: ethtool -K eth0 tso off gso off gro off (disable offload)
Update OpenSSL on both client and server to 3.x
Monitor uptime via Enterno Monitor — see failure patterns

Check SSL Certificate →

Example: Proper nginx TLS config

server {
    listen 443 ssl http2;
    server_name example.com;

    ssl_certificate     /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;

    ssl_protocols       TLSv1.2 TLSv1.3;
    ssl_ciphers         ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;
    ssl_prefer_server_ciphers off;

    ssl_stapling        on;
    ssl_stapling_verify on;
}

Related SSL Errors

CertificateExpiry, issuer, domains (SAN)

ChainIntermediate and root CA validation

TLS ProtocolTLS version and cipher suite

VulnerabilitiesHeartbleed, POODLE, weak ciphers

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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.

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DV vs OV vs EV Certificates

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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.

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How-to

Glossary

Research

TLS Cipher Suites 2026: Distribution Report

Errors

Alternatives

Frequently Asked Questions

What is a MAC in TLS?

Message Authentication Code — a cryptographic hash embedded in every TLS record. It verifies data integrity in transit. Bad MAC = data was corrupted.

Is this an attack?

Usually not. Mostly hardware/software bugs. But constant bad MACs can hint at a MITM attack (very rare).

Why does AV break things?

TLS inspection decrypts traffic, injects its own cert, re-encrypts. Bugs → MAC does not match.

Only in mobile browser — why?

Mobile networks often have lower MTU (1400–1460). Desktop over WiFi — 1500. The delta → fragmentation at the TLS layer.