3 files changed, 17 insertions, 3 deletions
diff --git a/modules/caddytls/acmeissuer.go b/modules/caddytls/acmeissuer.go
index 9dfeff724..29a5954e7 100644
--- a/modules/caddytls/acmeissuer.go
+++ b/modules/caddytls/acmeissuer.go
@@ -28,7 +28,7 @@ import (
 
 	"github.com/caddyserver/certmagic"
 	"github.com/caddyserver/zerossl"
-	"github.com/mholt/acmez/v2/acme"
+	"github.com/mholt/acmez/v3/acme"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 
diff --git a/modules/caddytls/automation.go b/modules/caddytls/automation.go
index f6a535077..1bc86020d 100644
--- a/modules/caddytls/automation.go
+++ b/modules/caddytls/automation.go
@@ -25,7 +25,7 @@ import (
 	"strings"
 
 	"github.com/caddyserver/certmagic"
-	"github.com/mholt/acmez/v2"
+	"github.com/mholt/acmez/v3"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 
diff --git a/modules/caddytls/connpolicy.go b/modules/caddytls/connpolicy.go
index 9332cf2ed..d9fc6bcfe 100644
--- a/modules/caddytls/connpolicy.go
+++ b/modules/caddytls/connpolicy.go
@@ -26,7 +26,7 @@ import (
 	"os"
 	"strings"
 
-	"github.com/mholt/acmez/v2"
+	"github.com/mholt/acmez/v3"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 
@@ -350,6 +350,20 @@ func (p *ConnectionPolicy) buildStandardTLSConfig(ctx caddy.Context) error {
 		if err := p.ClientAuthentication.ConfigureTLSConfig(cfg); err != nil {
 			return fmt.Errorf("configuring TLS client authentication: %v", err)
 		}
+
+		// Prevent privilege escalation in case multiple vhosts are configured for
+		// this TLS server; we could potentially figure out if that's the case, but
+		// that might be complex to get right every time. Actually, two proper
+		// solutions could leave tickets enabled, but I am not sure how to do them
+		// properly without significant time investment; there may be new Go
+		// APIs that alloaw this (Wrap/UnwrapSession?) but I do not know how to use
+		// them at this time. TODO: one of these is a possible future enhancement:
+		// A) Prevent resumptions across server identities (certificates): binding the ticket to the
+		// certificate we would serve in a full handshake, or even bind a ticket to the exact SNI
+		// it was issued under (though there are proposals for session resumption across hostnames).
+		// B) Prevent resumptions falsely authenticating a client: include the realm in the ticket,
+		// so that it can be validated upon resumption.
+		cfg.SessionTicketsDisabled = true
 	}
 
 	if p.InsecureSecretsLog != "" {