ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY

Enterno.io Editorial Team

By Anatoly Oshmanovsky · Updated Apr 18, 2026

Key idea:

ERR_SSL_WEAK_SERVER_EPHEMERAL_DH_KEY — Chrome detected the server using a Diffie-Hellman ephemeral key below 1024 bits (Logjam attack, 2015). Precomputation lets an attacker decrypt traffic. Fix: raise DH group to 2048 bits, or move to ECDHE (elliptic curve). nginx: ssl_dhparam with a freshly generated 2048-bit file + cipher list without DHE.

Below: causes, fixes, FAQ.

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Common Causes

Old nginx/Apache with default 1024-bit DH params
Unused ssl_dhparam — OpenSSL/Java default 1024-bit
Cipher list contains DHE-* (no EC)
Legacy Java server with DH 512
OpenSSL < 1.0.2 with weak defaults

Step-by-Step Fix

Generate 2048-bit DH: openssl dhparam -out dhparam.pem 2048 (5-10 minutes)
nginx: ssl_dhparam /etc/ssl/dhparam.pem;
Prefer ECDHE: ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256;
Or drop DHE entirely (ECDHE only)
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Related SSL Errors

CertificateExpiry, issuer, domains (SAN)

ChainIntermediate and root CA validation

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VulnerabilitiesHeartbleed, POODLE, weak ciphers

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

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

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

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

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Research

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Errors

Frequently Asked Questions

What is Logjam?

2015 attack: precomputed 1024-bit DH group enables MITM at ~$100k (state actor). All major browsers reject < 1024 bit.

Is 4096-bit better than 2048?

More CPU cost for marginal gain (NIST SP 800-131A: 2048 secure through 2030+). 2048 is the recommended baseline.

ECDHE replaces DHE?

Yes, ECDHE P-256 is faster + secure. Modern TLS configs use ECDHE only and drop DHE entirely.

Reissue cert?

No, Logjam fix is server TLS config, the cert itself is unchanged.