CVE-2026-56821

### Summary `OcspServerCertificateValidator` flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as `VALID`, letting an on-path attacker replay a stale GOOD response to bypass revocation of a since-revoked certificate. ### Details In `io.netty.handler.ssl.ocsp.OcspServerCertificateValidator#userEventTriggered` the freshness check has no `return`, so execution falls through and a `VALID` `OcspValidationEvent` is still fired: ```java if (!(current.after(response.getThisUpdate()) && current.before(response.getNextUpdate()))) { ctx.fireExceptionCaught(new IllegalStateException("OCSP Response is out-of-date")); } ``` Nonce validation is optional and off by default, so freshness is the only replay defense — and it is not enforced. Additionally `getNextUpdate()` may be `null`, making `current.before(null)` throw `NullPointerException`. https://datatracker.ietf.org/doc/html/rfc6960#section-3.2 ``` 5. The time at which the status being indicated is known to be correct (thisUpdate) is sufficiently recent; 6. When available, the time at or before which newer information will be available about the status of the certificate (nextUpdate) is greater than the current time. ``` ### PoC Add the test below to `io.netty.handler.ssl.ocsp.OcspServerCertificateValidatorTest` ```java @Test void staleOcspResponseIsRejected() throws Exception { X509Bundle caRoot = new CertificateBuilder() .algorithm(CertificateBuilder.Algorithm.rsa2048) .subject("CN=TrustedRootCA") .setIsCertificateAuthority(true) .buildSelfSigned(); GeneralName ocspName = new GeneralName(GeneralName.uniformResourceIdentifier, "http://localhost/"); AuthorityInformationAccess aia = new AuthorityInformationAccess( new AccessDescription(AccessDescription.id_ad_ocsp, ocspName)); X509Bundle targetCert = new CertificateBuilder() .algorithm(CertificateBuilder.Algorithm.rsa2048) .subject("CN=TargetServer") .addExtensionOctetString("1.3.6.1.5.5.7.1.1", false, aia.getEncoded()) .buildIssuedBy(caRoot); Date past = new Date(System.currentTimeMillis() - TimeUnit.DAYS.toMillis(7)); CertificateID certId = new CertificateID( new JcaDigestCalculatorProviderBuilder().build().get(CertificateID.HASH_SHA1), new JcaX509CertificateHolder(caRoot.getCertificate()), targetCert.getCertificate().getSerialNumber()); BasicOCSPRespBuilder respBuilder = new BasicOCSPRespBuilder( new RespID(new JcaX509CertificateHolder(caRoot.getCertificate()).getSubject())); respBuilder.addResponse(certId, CertificateStatus.GOOD, past, past); BasicOCSPResp expiredBasicResp = respBuilder.build( new JcaContentSignerBuilder("SHA256withRSA").build(caRoot.getKeyPair().getPrivate()), new X509CertificateHolder[0], past); final byte[] responseEncoded = new OCSPRespBuilder() .build(OCSPRespBuilder.SUCCESSFUL, expiredBasicResp).getEncoded(); IoTransport defaultTransport = createDefaultTransport(); IoTransport mockTransport = IoTransport.create(defaultTransport.eventLoop(), () -> { NioSocketChannel channel = new NioSocketChannel(); channel.pipeline().addFirst(new ChannelOutboundHandlerAdapter() { @Override public void connect(ChannelHandlerContext ctx, SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) { promise.setSuccess(); ctx.executor().execute(() -> { 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); }); } }); return channel; }, defaultTransport.datagramChannel()); SslContext serverSslCtx = SslContextBuilder .forServer(targetCert.getKeyPair().getPrivate(), targetCert.getCertificate(), caRoot.getCertificate()) .build(); Channel serverChannel = new ServerBootstrap() .group(defaultTransport.eventLoop()) .channel(NioServerSocketChannel.class) .childHandler(new ChannelInitializer<SocketChannel>() { @Override protected void initChannel(SocketChannel ch) { ch.pipeline().addLast(serverSslCtx.newHandler(ch.alloc())); } }) .bind(0).sync().channel(); int serverPort = ((InetSocketAddress) serverChannel.localAddress()).getPort(); AtomicBoolean validEventFired = new AtomicBoolean(); AtomicReference<Throwable> caughtException = new AtomicReference<>(); CountDownLatch latch = new CountDownLatch(1); DnsNameResolver resolver = OcspServerCertificateValidator.createDefaultResolver(mockTransport); SslContext clientSslCtx = SslContextBuilder.forClient() .trustManager(InsecureTrustManagerFactory.INSTANCE) .build(); new Bootstrap() .group(defaultTransport.eventLoop()) .channel(NioSocketChannel.class) .handler(new ChannelInitializer<SocketChannel>() { @Override protected void initChannel(SocketChannel ch) { ch.pipeline().addLast(clientSslCtx.newHandler(ch.alloc(), "127.0.0.1", serverPort)); ch.pipeline().addLast( new OcspServerCertificateValidator(true, false, mockTransport, resolver)); ch.pipeline().addLast(new ChannelInboundHandlerAdapter() { @Override public void userEventTriggered(ChannelHandlerContext ctx, Object evt) { if (evt instanceof OcspValidationEvent && ((OcspValidationEvent) evt).response().status() == OcspResponse.Status.VALID) { validEventFired.set(true); } ctx.fireUserEventTriggered(evt); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { caughtException.compareAndSet(null, cause); ctx.channel().close(); latch.countDown(); } }); } }) .connect("127.0.0.1", serverPort).sync(); assertTrue(latch.await(5, TimeUnit.SECONDS)); assertFalse(validEventFired.get(), "OcspValidationEvent(VALID) must not be emitted for a stale OCSP response"); assertNotNull(caughtException.get()); assertInstanceOf(IllegalStateException.class, caughtException.get()); serverChannel.close().sync(); resolver.close(); } ``` ### Impact Certificate revocation bypass via replay of an expired OCSP response. Any application using `OcspServerCertificateValidator` is affected; a revoked certificate can be accepted.

### Summary `OcspServerCertificateValidator` flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as `VALID`, letting an on-path attacker replay a stale GOOD response to bypass revocation of a since-revoked certificate. ### Details In `io.netty.handler.ssl.ocsp.OcspServerCertificateValidator#userEventTriggered` the freshness check has no `return`, so execution falls through and a `VALID` `OcspValidationEvent` is still fired: ```java if (!(current.after(response.getThisUpdate()) && current.before(response.getNextUpdate()))) { ctx.fireExceptionCaught(new IllegalStateException("OCSP Response is out-of-date")); } ``` Nonce validation is optional and off by default, so freshness is the only replay defense — and it is not enforced. Additionally `getNextUpdate()` may be `null`, making `current.before(null)` throw `NullPointerException`. https://datatracker.ietf.org/doc/html/rfc6960#section-3.2 ``` 5. The time at which the status being indicated is known to be correct (thisUpdate) is sufficiently recent; 6. When available, the time at or before which newer information will be available about the status of the certificate (nextUpdate) is greater than the current time. ``` ### PoC Add the test below to `io.netty.handler.ssl.ocsp.OcspServerCertificateValidatorTest` ```java @Test void staleOcspResponseIsRejected() throws Exception { X509Bundle caRoot = new CertificateBuilder() .algorithm(CertificateBuilder.Algorithm.rsa2048) .subject("CN=TrustedRootCA") .setIsCertificateAuthority(true) .buildSelfSigned(); GeneralName ocspName = new GeneralName(GeneralName.uniformResourceIdentifier, "http://localhost/"); AuthorityInformationAccess aia = new AuthorityInformationAccess( new AccessDescription(AccessDescription.id_ad_ocsp, ocspName)); X509Bundle targetCert = new CertificateBuilder() .algorithm(CertificateBuilder.Algorithm.rsa2048) .subject("CN=TargetServer") .addExtensionOctetString("1.3.6.1.5.5.7.1.1", false, aia.getEncoded()) .buildIssuedBy(caRoot); Date past = new Date(System.currentTimeMillis() - TimeUnit.DAYS.toMillis(7)); CertificateID certId = new CertificateID( new JcaDigestCalculatorProviderBuilder().build().get(CertificateID.HASH_SHA1), new JcaX509CertificateHolder(caRoot.getCertificate()), targetCert.getCertificate().getSerialNumber()); BasicOCSPRespBuilder respBuilder = new BasicOCSPRespBuilder( new RespID(new JcaX509CertificateHolder(caRoot.getCertificate()).getSubject())); respBuilder.addResponse(certId, CertificateStatus.GOOD, past, past); BasicOCSPResp expiredBasicResp = respBuilder.build( new JcaContentSignerBuilder("SHA256withRSA").build(caRoot.getKeyPair().getPrivate()), new X509CertificateHolder[0], past); final byte[] responseEncoded = new OCSPRespBuilder() .build(OCSPRespBuilder.SUCCESSFUL, expiredBasicResp).getEncoded(); IoTransport defaultTransport = createDefaultTransport(); IoTransport mockTransport = IoTransport.create(defaultTransport.eventLoop(), () -> { NioSocketChannel channel = new NioSocketChannel(); channel.pipeline().addFirst(new ChannelOutboundHandlerAdapter() { @Override public void connect(ChannelHandlerContext ctx, SocketAddress remoteAddress, SocketAddress localAddress, ChannelPromise promise) { promise.setSuccess(); ctx.executor().execute(() -> { 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); }); } }); return channel; }, defaultTransport.datagramChannel()); SslContext serverSslCtx = SslContextBuilder .forServer(targetCert.getKeyPair().getPrivate(), targetCert.getCertificate(), caRoot.getCertificate()) .build(); Channel serverChannel = new ServerBootstrap() .group(defaultTransport.eventLoop()) .channel(NioServerSocketChannel.class) .childHandler(new ChannelInitializer<SocketChannel>() { @Override protected void initChannel(SocketChannel ch) { ch.pipeline().addLast(serverSslCtx.newHandler(ch.alloc())); } }) .bind(0).sync().channel(); int serverPort = ((InetSocketAddress) serverChannel.localAddress()).getPort(); AtomicBoolean validEventFired = new AtomicBoolean(); AtomicReference<Throwable> caughtException = new AtomicReference<>(); CountDownLatch latch = new CountDownLatch(1); DnsNameResolver resolver = OcspServerCertificateValidator.createDefaultResolver(mockTransport); SslContext clientSslCtx = SslContextBuilder.forClient() .trustManager(InsecureTrustManagerFactory.INSTANCE) .build(); new Bootstrap() .group(defaultTransport.eventLoop()) .channel(NioSocketChannel.class) .handler(new ChannelInitializer<SocketChannel>() { @Override protected void initChannel(SocketChannel ch) { ch.pipeline().addLast(clientSslCtx.newHandler(ch.alloc(), "127.0.0.1", serverPort)); ch.pipeline().addLast( new OcspServerCertificateValidator(true, false, mockTransport, resolver)); ch.pipeline().addLast(new ChannelInboundHandlerAdapter() { @Override public void userEventTriggered(ChannelHandlerContext ctx, Object evt) { if (evt instanceof OcspValidationEvent && ((OcspValidationEvent) evt).response().status() == OcspResponse.Status.VALID) { validEventFired.set(true); } ctx.fireUserEventTriggered(evt); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { caughtException.compareAndSet(null, cause); ctx.channel().close(); latch.countDown(); } }); } }) .connect("127.0.0.1", serverPort).sync(); assertTrue(latch.await(5, TimeUnit.SECONDS)); assertFalse(validEventFired.get(), "OcspValidationEvent(VALID) must not be emitted for a stale OCSP response"); assertNotNull(caughtException.get()); assertInstanceOf(IllegalStateException.class, caughtException.get()); serverChannel.close().sync(); resolver.close(); } ``` ### Impact Certificate revocation bypass via replay of an expired OCSP response. Any application using `OcspServerCertificateValidator` is affected; a revoked certificate can be accepted.