SSL version or cipher mismatch
ERR_SSL_VERSION_OR_CIPHER_MISMATCHThe browser and server share no common TLS version or cipher suite, so they can't agree on how to encrypt the connection.
What it means
A TLS handshake needs both sides to support at least one common protocol version and one common cipher suite. ERR_SSL_VERSION_OR_CIPHER_MISMATCH means that overlap is empty. Modern browsers have dropped old, weak protocols like TLS 1.0 and 1.1 and insecure ciphers, so a server that only offers those has nothing left to negotiate with an up-to-date browser.
When it happens
This usually involves an older server stuck on deprecated TLS versions or weak ciphers, hit by a current browser that refuses them. It also appears the other way around: an old browser or device that doesn't support TLS 1.2 or 1.3 trying to reach a modern, hardened server. Misconfigured cipher lists after a security hardening pass can accidentally leave no overlap with real-world clients.
How to fix it
- Check which TLS versions and ciphers the server offers, then enable TLS 1.2 and TLS 1.3 with a modern cipher suite.
- Avoid over-restricting the cipher list so tightly that common, current clients are excluded.
- If the problem is an old client, update the browser or operating system so it supports modern TLS.
- Retest the handshake after each config change to confirm a working overlap exists.
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Related errors
ERR_SSL_PROTOCOL_ERRORThe TLS handshake fell apart before a secure connection could form, often from a protocol mismatch or a broken server config.
ERR_CERT_WEAK_SIGNATURE_ALGORITHMThe certificate was signed with an algorithm now considered too weak to trust, such as SHA-1.
NET::ERR_CERT_AUTHORITY_INVALIDThe browser can't trace the certificate back to a trusted authority, which is what happens with self-signed certs or a missing intermediate.