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fix: skip TLS 1.2 resumption on extended_master_secret mismatch #417

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fix: skip TLS 1.2 resumption on extended_master_secret mismatch #417

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9 changes: 9 additions & 0 deletions handshake_client.go
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Original file line number Diff line number Diff line change
Expand Up @@ -457,6 +457,15 @@ func (c *Conn) loadSession(hello *clientHelloMsg) (
}

if session.version != VersionTLS13 {
// [uTLS] TLS 1.2 resumption requires the cached session EMS state to
// match the new ClientHello. A ClientHelloSpec may omit the
// extended_master_secret extension, in which case a server holding an
// EMS session will reject the handshake. Skip resumption instead, so
// the dial proceeds with the selected spec.
if session.extMasterSecret != hello.extendedMasterSecret {
return nil, nil, nil, nil
}

// In TLS 1.2 the cipher suite must match the resumed session. Ensure we
// are still offering it.
if mutualCipherSuite(hello.cipherSuites, session.cipherSuite) == nil {
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7 changes: 7 additions & 0 deletions u_parrots.go
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Original file line number Diff line number Diff line change
Expand Up @@ -3045,6 +3045,13 @@ func (uconn *UConn) ApplyPreset(p *ClientHelloSpec) error {
uconn.echCtx = ech
hello := uconn.HandshakeState.Hello

// [uTLS] A preset must control TLS 1.2 extended_master_secret through its
// extension list. The default ClientHello enables EMS unconditionally, so
// clear it here and let ExtendedMasterSecretExtension.writeToUConn set it
// again only when the spec actually carries the extension. The EMS state
// check in Conn.loadSession depends on this being accurate.
hello.Ems = false

switch len(hello.Random) {
case 0:
hello.Random = make([]byte, 32)
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