GHSA-wc96-39fc-566f — Netty: TOCTOU in OcspServerCertificateValidator

Affected: Maven: io.netty:netty-handler-ssl-ocsp

### Summary Netty's OcspServerCertificateValidator forwards the SslHandshakeCompletionEvent before the asynchronous OCSP validation completes. This allows the client's downstream handlers to send sensitive application data (e.g., HTTP requests) to a revoked server before the channel is closed by the OCSP check.

### Details In `io.netty.handler.ssl.ocsp.OcspServerCertificateValidator#userEventTriggered`, when an `SslHandshakeCompletionEvent` is received, the validator immediately calls `ctx.fireUserEventTriggered(evt)`. It then initiates an asynchronous OCSP query using `OcspClient.query`.

Because the handshake completion event is forwarded immediately, downstream handlers in the client's pipeline are notified that the TLS handshake is successful. They may then begin reading and processing incoming application data or sending outgoing data. If the OCSP response later indicates the server's certificate is REVOKED, the validator closes the channel, but by this time, the client may have already leaked sensitive data to a revoked server or processed malicious responses from it.

### PoC

```java @Test public void test() throws Exception { EventLoopGroup group = new MultiThreadIoEventLoopGroup(NioIoHandler.newFactory()); try { OCSPRespBuilder respBuilder = new OCSPRespBuilder(); OCSPResp response = respBuilder.build(OCSPRespBuilder.INTERNAL_ERROR, null); byte[] responseEncoded = response.getEncoded();

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GHSA-wc96-39fc-566f — Netty: TOCTOU in OcspServerCertificateValidator