crypto/tls: TLS 1.3 handshake timeout with tip, Go 1.26 can connect successfully

[kevinburke]

What version of Go are you using (go version)?

$ go version
go version go1.27-devel_bfbbe9667e Fri May 22 15:49:08 2026 -0700 darwin/arm64

Does this issue reproduce with the latest release?

No

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
AR='ar'
CC='clang'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='clang++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/Users/kevin/Library/Caches/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/Users/kevin/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/gh/xgxt3m8d5kd3353q6wyl6c1m0000gn/T/go-build927103055=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/Users/kevin/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPACKAGESDRIVER=''
GOPATH='/Users/kevin'
GOPRIVATE=''
GOPROXY='direct'
GOROOT='/Users/kevin/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/kevin/Library/Application Support/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/kevin/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.27-devel_bfbbe9667e Fri May 22 15:49:08 2026 -0700'
GOWORK=''
PKG_CONFIG='pkg-config'
GOROOT/bin/go version: go version go1.27-devel_bfbbe9667e Fri May 22 15:49:08 2026 -0700 darwin/arm64
GOROOT/bin/go tool compile -V: compile version go1.27-devel_bfbbe9667e Fri May 22 15:49:08 2026 -0700
uname -v: Darwin Kernel Version 25.3.0: Wed Jan 28 20:54:46 PST 2026; root:xnu-12377.91.3~2/RELEASE_ARM64_T6000
ProductName:		macOS
ProductVersion:		26.3.1
ProductVersionExtra:	(a)
BuildVersion:		25D771280a
lldb --version: lldb-2100.0.16.4
Apple Swift version 6.3 (swiftlang-6.3.0.123.5 clang-2100.0.123.102)

What did you do?

I can't connect to https://oakland.granicus.com/ with Go 1.27 at tip, it tries to negotiate TLS 1.3 and then just errors with "handshake timeout".

Go 1.26 is able to complete a connection (as is my browser, curl, etc.)

[kevinburke]

Bisected to commit c74ba7d. Here's the bisect script.

package main

import (
	"context"
	"io"
	"log/slog"
	"net/http"
	"os"
	"time"
)

const userAgent = "go-bisect-oakland-tls/0.1"

func main() {
	logger := slog.New(slog.NewTextHandler(os.Stderr, nil))

	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, "https://oakland.granicus.com", nil)
	if err != nil {
		logger.Error("create request", "err", err)
		os.Exit(2)
	}
	req.Header.Set("User-Agent", userAgent)

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		logger.Error("request failed", "err", err)
		os.Exit(1)
	}
	defer resp.Body.Close()

	_, _ = io.Copy(io.Discard, io.LimitReader(resp.Body, 4096))
	logger.Info("request succeeded", "status", resp.Status)
}

[gabyhelp]

Related Issues

• crypto/x509: crash on macOS Tahoe 26 #75684 (closed)
• crypto/tls: TLS handshake timeout #44267 (closed)
• crypto/tls: handshake failure with www.ksecurity.or.kr #64370 (closed)
• crypto/tls: SMTP connection timeout in Go Version 1.23 #71257 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

cc @FiloSottile

[FiloSottile]

This is an extremely weird failure.

The following changes make it work:

1. Removing the ML-DSA signature algorithms.
2. Moving any other existing signature algorithm before the ML-DSA ones (including rarely implemented ones like Ed25519).
3. Removing signature_algorithms_cert but leaving ML-DSA in the first position of signature_algorithms.

Changing the ML-DSA signature algorithms to non-existing ones does not make it work.

I honestly can't imagine what that implementation is doing, but I was contemplating dropping signature_algorithms_cert anyway, which no one else is sending anyway.

[kevinburke]

Do you have any advice for the server maintainer? Granicus/legistar powers a lot of public agency agendas across the United States, I could try to reach their security/server team

[FiloSottile]

It would actually be useful to know what they are doing, or what vendor this is. The advice is "implement the spec correctly" but it's probably more useful to collect information first. Maybe we can get it fixed upstream. I think it's the first instance of signature algorithm intolerance we have seen in the wild.