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EOF occurred in violation of protocol Python: ssl.SSLEOFError: EOF occurred in violation of protocol (_ssl.c:2396)

SSL / TLS · layer 2, Network

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1 · On your device 2 · Network 3 · Edge & web server 4 · Application & API 7 · Build & delivery
EOF occurred in violation of protocol — Python: ssl.SSLEOFError: EOF occurred in violation of protocol (_ssl.c:2396) (SSL / TLS)EOF occurre…cURL error 35 — cURL error 35: OpenSSL SSL_connect: SSL_ERROR_SYSCALL in connection to host:443 (PHP)cURL error 35CERTIFICATE_VERIFY_FAILED — SSL: CERTIFICATE_VERIFY_FAILED / unable to get local issuer certificate (API)CERTIFICATE_VERIFY_…Received fatal alert: handshake_failure — Java: javax.net.ssl.SSLHandshakeException: Received fatal alert: handshake_failure (SSL / TLS)Received fatal aler…gRPC: Ssl handshake failed / authentication handshake failed — gRPC: rpc error: code = Unavailable desc = connection error: desc = "transport: authentication handshake failed: x509: certificate signed by unknown authority" (SSL / TLS)gRPC: Ssl handshake…sslv3 alert handshake failure — OpenSSL: error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure (SSL alert number 40) (SSL / TLS)sslv3 alert handsha…tlsv1 unrecognized name (SNI) — OpenSSL: SSL alert number 112 — tlsv1 unrecognized name (SSL / TLS)tlsv1 unrecognized …HTTPSConnectionPool: Max retries exceeded (SSLError) — Python requests: HTTPSConnectionPool(host='api.example.com', port=443): Max retries exceeded with url: /v1 (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] ...'))) (SSL / TLS)HTTPSConnectionPool…Git SSL certificate problem — fatal: unable to access 'https://…': SSL certificate problem: unable to get local issuer certificate (Git)Git SSL certificate…PKIX path building failed — javax.net.ssl.SSLHandshakeException: PKIX path building failed: unable to find valid certification path to requested target (Java)PKIX path building …SocketException reset — java.net.SocketException: Connection reset (Java)SocketException res…502 — HTTP 502 Bad Gateway (HTTP)502Failed to fetch — TypeError: Failed to fetch / NetworkError when attempting to fetch resource (JavaScript)Failed to fetch520 — Cloudflare Error 520: Web Server Returned an Unknown Error (Cloudflare)520tlsv1 alert protocol version — OpenSSL: error:14094410 / SSL alert number 70 — tlsv1 alert protocol version (SSL / TLS)tlsv1 alert protoco…No subject alternative names present — Java: javax.net.ssl.SSLHandshakeException: No subject alternative names matching IP address 10.0.0.5 found (SSL / TLS)No subject alternat…Keystore was tampered with, or password was incorrect — Java keytool: java.io.IOException: Keystore was tampered with, or password was incorrect (SSL / TLS)Keystore was tamper…x509: certificate signed by unknown authority — Go: x509: certificate signed by unknown authority (Go)x509: certificate s…x509: certificate is valid for X, not Y — Go: x509: certificate is valid for www.example.com, not api.example.com (Go)x509: certificate i…SSL routines: wrong version number — OpenSSL: error:1408F10B:SSL routines:ssl3_get_record:wrong version number (SSL / TLS)SSL routines: wrong…SSL_ERROR_NO_CYPHER_OVERLAP — Firefox: Secure Connection Failed — SSL_ERROR_NO_CYPHER_OVERLAP (no common cipher) (Browser)SSL_ERROR_NO_CYPHER…unable to get local issuer certificate — OpenSSL: error:num=20:unable to get local issuer certificate / SSL: CERTIFICATE_VERIFY_FAILED (SSL / TLS)unable to get local…ca md too weak / ee key too small — OpenSSL: error:0A00018E:SSL routines::ca md too weak / error:140AB18F:SSL routines:SSL_CTX_use_certificate:ee key too small (SSL / TLS)ca md too weak / ee…SSL_ERROR_BAD_CERT_DOMAIN — Firefox: Websites prove their identity via certificates — the certificate is only valid for other names. Error code: SSL_ERROR_BAD_CERT_DOMAIN (SSL / TLS)SSL_ERROR_BAD_CERT_…no "ssl_certificate" is defined for the "listen ... ssl" directive — Nginx: [emerg] no "ssl_certificate" is defined for the "listen ... ssl" directive in /etc/nginx/sites-enabled/default:3 (SSL / TLS)no "ssl_certificate…Timeout during connect (likely firewall problem) — Let's Encrypt: Fetching http://example.com/.well-known/acme-challenge/token: Timeout during connect (likely firewall problem) (SSL / TLS)Timeout during conn…1003 — Cloudflare Error 1003: Direct IP access not allowed (Cloudflare)10031013 — Cloudflare Error 1013: HTTP hostname and TLS SNI hostname mismatch (Cloudflare)1013SSLCertificateFile: file does not exist — Apache: AH02240: Server should be SSL-aware but has no certificate configured / SSLCertificateFile: file '/etc/ssl/x.crt' does not exist or is empty (SSL / TLS)SSLCertificateFile:…

Directly related (7)

cURL error 35PHP

cURL error 35: OpenSSL SSL_connect: SSL_ERROR_SYSCALL in connection to host:443

The TLS handshake failed — protocol/cipher mismatch, a proxy interfering, or the server closed the connection.

CERTIFICATE_VERIFY_FAILEDAPI

SSL: CERTIFICATE_VERIFY_FAILED / unable to get local issuer certificate

The client couldn’t verify the server’s TLS certificate chain, so it refused the HTTPS connection.

Received fatal alert: handshake_failureSSL / TLS

Java: javax.net.ssl.SSLHandshakeException: Received fatal alert: handshake_failure

The server rejected the Java client's TLS offer — no shared protocol/cipher, SNI issue or a required client certificate.

gRPC: Ssl handshake failed / authentication handshake failedSSL / TLS

gRPC: rpc error: code = Unavailable desc = connection error: desc = "transport: authentication handshake failed: x509: certificate signed by unknown authority"

A gRPC client could not complete TLS to the server — untrusted certificate, name mismatch, or plaintext/TLS mismatch.

sslv3 alert handshake failureSSL / TLS

OpenSSL: error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure (SSL alert number 40)

The server aborted the handshake with alert 40 — no acceptable parameters (cipher, signature algorithm, client certificate or SNI…

tlsv1 unrecognized name (SNI)SSL / TLS

OpenSSL: SSL alert number 112 — tlsv1 unrecognized name

The server did not recognise the hostname sent in SNI and rejected the handshake (or an alert/warning is logged).

HTTPSConnectionPool: Max retries exceeded (SSLError)SSL / TLS

Python requests: HTTPSConnectionPool(host='api.example.com', port=443): Max retries exceeded with url: /v1 (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] ...')))

The `requests` call failed during the TLS step and exhausted its retries; the real reason is in the nested SSLError text.

Two steps away (21)

Git SSL certificate problemGit

fatal: unable to access 'https://…': SSL certificate problem: unable to get local issuer certificate

Git doesn’t trust the HTTPS server’s certificate — corporate proxy, self-hosted Git with an internal CA, or outdated CA bundle.

PKIX path building failedJava

javax.net.ssl.SSLHandshakeException: PKIX path building failed: unable to find valid certification path to requested target

Java doesn’t trust the server’s certificate chain (self-signed, corporate proxy CA, or missing intermediate).

SocketException resetJava

java.net.SocketException: Connection reset

The remote side closed the TCP connection abruptly while Java was reading or writing.

502HTTP

HTTP 502 Bad Gateway

A proxy or gateway (Nginx, load balancer, CDN) got an invalid response — or no response — from the upstream server behind it.

Failed to fetchJavaScript

TypeError: Failed to fetch / NetworkError when attempting to fetch resource

The browser couldn’t complete the request at the network level — CORS, DNS, offline, blocked mixed content, or the server refused…

520Cloudflare

Cloudflare Error 520: Web Server Returned an Unknown Error

Cloudflare connected to your origin, but the origin returned an empty, unknown or invalid response.

tlsv1 alert protocol versionSSL / TLS

OpenSSL: error:14094410 / SSL alert number 70 — tlsv1 alert protocol version

The server rejected the TLS version your client offered, because it requires a newer (or older) protocol.

No subject alternative names presentSSL / TLS

Java: javax.net.ssl.SSLHandshakeException: No subject alternative names matching IP address 10.0.0.5 found

Java checks the hostname against the certificate's SANs and found no matching entry (for DNS names or IPs).

Keystore was tampered with, or password was incorrectSSL / TLS

Java keytool: java.io.IOException: Keystore was tampered with, or password was incorrect

keytool or the JVM could not open the keystore — wrong password, wrong file type, or damaged file.

x509: certificate signed by unknown authorityGo

Go: x509: certificate signed by unknown authority

The Go TLS client does not trust the CA that signed the server's certificate.

x509: certificate is valid for X, not YGo

Go: x509: certificate is valid for www.example.com, not api.example.com

The server's certificate does not list the hostname you connected to (SAN mismatch), or it has expired.

SSL routines: wrong version numberSSL / TLS

OpenSSL: error:1408F10B:SSL routines:ssl3_get_record:wrong version number

The peer did not answer with a TLS record — you spoke TLS to a plain HTTP/SMTP port (or the reverse), or a proxy intervened.

SSL_ERROR_NO_CYPHER_OVERLAPBrowser

Firefox: Secure Connection Failed — SSL_ERROR_NO_CYPHER_OVERLAP (no common cipher)

Firefox and the server share no TLS cipher suite, so the secure handshake cannot even start.

unable to get local issuer certificateSSL / TLS

OpenSSL: error:num=20:unable to get local issuer certificate / SSL: CERTIFICATE_VERIFY_FAILED

The client could not build a chain from the server's certificate to a CA it trusts — the issuer is missing locally or the server…

ca md too weak / ee key too smallSSL / TLS

OpenSSL: error:0A00018E:SSL routines::ca md too weak / error:140AB18F:SSL routines:SSL_CTX_use_certificate:ee key too small

OpenSSL's security level rejected a certificate signed with a weak hash (MD5/SHA-1) or with a small key (RSA < 2048).

SSL_ERROR_BAD_CERT_DOMAINSSL / TLS

Firefox: Websites prove their identity via certificates — the certificate is only valid for other names. Error code: SSL_ERROR_BAD_CERT_DOMAIN

The certificate does not include the hostname you typed.

no "ssl_certificate" is defined for the "listen ... ssl" directiveSSL / TLS

Nginx: [emerg] no "ssl_certificate" is defined for the "listen ... ssl" directive in /etc/nginx/sites-enabled/default:3

A server block listens with `ssl` but has no `ssl_certificate` and `ssl_certificate_key`.

Timeout during connect (likely firewall problem)SSL / TLS

Let's Encrypt: Fetching http://example.com/.well-known/acme-challenge/token: Timeout during connect (likely firewall problem)

The ACME validation server could not reach your server on port 80 within the timeout.

1003Cloudflare

Cloudflare Error 1003: Direct IP access not allowed

The request went to a Cloudflare IP address directly (or with a Host header for a domain not on Cloudflare).

1013Cloudflare

Cloudflare Error 1013: HTTP hostname and TLS SNI hostname mismatch

The TLS SNI (the hostname used for the certificate) differs from the HTTP Host header in the same request.

SSLCertificateFile: file does not existSSL / TLS

Apache: AH02240: Server should be SSL-aware but has no certificate configured / SSLCertificateFile: file '/etc/ssl/x.crt' does not exist or is empty

Apache cannot find the certificate or key file named in its configuration, or `SSLEngine on` is set without any certificate.

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