Don't use IP literals for TLS SNI - #186
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An authority containing an IP literal (e.g. a .dns target created with an IP address, common when callers resolve addresses themselves) was passed to the TLS handshake as the SNI server hostname. RFC 6066 § 3 only permits DNS hostnames in SNI and NIOSSL enforces this, so such connections failed with cannotUseIPAddressInSNI before the handshake started. SocketAddress.sniHostname already applies this rule; the authority-derived hostname now does too: IP literals (bare v4/v6, with a port, or bracketed v6) yield no SNI instead of a handshake failure.
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glbrntt
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One tiny change but looks good otherwise
| // Undo the bracketing applied to IPv6 addresses in authorities | ||
| // (e.g. "[2001:db8::1]:443"). | ||
| if host.utf8.first == UInt8(ascii: "["), host.utf8.last == UInt8(ascii: "]") { | ||
| host = String(host.dropFirst().dropLast()) |
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Square brackets imply an IPv6 address so we can just return nil here, I think.
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Done — brackets now return nil directly (and host became a let).
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Apologies for missing this: it looks like the CI is failing because of a Swift issue: swiftlang/swift#85427 We might be able to workaround it with a patch to swift-nio: apple/swift-nio#3696 |
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Motivation
When a connection's authority contains an IP literal — e.g. a
.dnstarget created with an IP address, which is common when callers resolve addresses themselves (multi-homed servers, NAT64 synthesis on mobile clients, health checks by address) — the literal is passed to the TLS handshake as the SNI server hostname. RFC 6066 § 3 only permits DNS hostnames in SNI, and NIOSSL enforces this: the connection fails withNIOSSLExtraError.cannotUseIPAddressInSNIbefore the handshake starts, surfacing to callers asunavailable: Could not establish a connection….SocketAddress.sniHostnamealready applies exactly this rule ("Literal IP addresses aren't allowed in the SNI hostname") — but the authority-derived hostname takes precedence over it and doesn't.Modifications
Connection.sanitizeAuthorityForSNInow returnsnilfor IP literals — bare IPv4/IPv6, with a trailing port, or bracketed IPv6 — after its existing port-stripping. The literal check runs before port-stripping too, since that logic would otherwise mangle bare IPv6 literals like::1.sniServerHostnamethen falls back through the existing?? self.address.sniHostnamepath, so such connections are made without SNI instead of failing.Result
Dialling an IP literal over TLS connects (subject to the configured certificate verification) instead of failing with
cannotUseIPAddressInSNI. Hostname authorities are unaffected.Extended the existing
testAuthorityIsSanitizedharness with IP-literal cases (127.0.0.1,127.0.0.1:9443,::1,[2001:db8::1]:443), all expecting no SNI.