Netty CVE-2026-56821
HIGHSeverity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Network-reachable and unauthenticated (AV:N/PR:N) but AC:H because the attacker needs on-path position plus a revoked cert and a pre-captured signed GOOD response; bypassing TLS auth yields C:H/I:H, A:N (NPE DoS scored separately).
Primary rating from Vendor (https://github.com/netty/netty).
CVSS VectorVendor: https://github.com/netty/netty
Lifecycle Timeline
3Blast Radius
ecosystem impact- 74 maven packages depend on io.netty:netty-handler-ssl-ocsp (2 direct, 72 indirect)
Ecosystem-wide dependent count for version 4.2.0.Final.
DescriptionCVE.org
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OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD response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:
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ctx.fireExceptionCaught(new IllegalStateException("OCSP Response is out-of-date"));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
@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.
AnalysisAI
Certificate revocation bypass in the Netty netty-handler-ssl-ocsp module (versions before 4.1.136.Final, and 4.2.0.Final through 4.2.15.Final) lets an on-path attacker replay a stale, expired-but-GOOD OCSP response to make OcspServerCertificateValidator accept a certificate that has since been revoked. A missing return statement after the freshness check causes execution to fall through and still fire a VALID OcspValidationEvent even after flagging the response as out-of-date. Publicly available exploit code exists (a PoC unit test is embedded in the GHSA advisory); the issue is not listed in CISA KEV and no EPSS score was provided.
Technical ContextAI
The flaw lives in io.netty.handler.ssl.ocsp.OcspServerCertificateValidator#userEventTriggered, part of Netty's optional OCSP (Online Certificate Status Protocol, RFC 6960) stapling/validation support built on Bouncy Castle. Per RFC 6960 section 3.2, a client must confirm both that thisUpdate is sufficiently recent and that nextUpdate is greater than the current time before trusting a status. The code performs this check - if the current time is not within the thisUpdate/nextUpdate window it raises IllegalStateException('OCSP Response is out-of-date') via fireExceptionCaught - but omits a return, so the method continues and still emits a VALID event. Because nonce validation is optional and disabled by default, temporal freshness is the only defense against replay, and it is not enforced. This maps to CWE-299 (Improper Check for Certificate Revocation). A secondary defect exists: getNextUpdate() may return null, causing current.before(null) to throw NullPointerException, a potential crash/DoS path.
RemediationAI
Vendor-released patch: upgrade to 4.1.136.Final (for 4.1.x deployments) or 4.2.16.Final (for 4.2.x deployments), per the release notes at https://github.com/netty/netty/releases/tag/netty-4.1.136.Final and https://github.com/netty/netty/releases/tag/netty-4.2.16.Final and the advisory at https://github.com/netty/netty/security/advisories/GHSA-g7hg-vrcf-mvmr. If you cannot upgrade immediately, enable OCSP nonce validation where your deployment supports it so that replayed responses are rejected on nonce mismatch rather than relying solely on freshness (trade-off: requires OCSP responders that echo nonces, and not all responders do). As a stronger compensating control, do not depend on OcspServerCertificateValidator as the sole revocation mechanism - pair it with short-lived certificates or an independent CRL/OCSP check outside the vulnerable code path - and shorten certificate lifetimes to reduce the window in which a revoked-but-cached GOOD response remains replayable. Upgrading is strongly preferred, as the workarounds only narrow rather than close the gap.
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View allSame technique Authentication Bypass
View allVendor StatusVendor
SUSE
Severity: Important| Product | Status |
|---|---|
| SUSE Linux Enterprise Desktop 15 SP7 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP7 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP7 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP7 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP7 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP7 | Not-Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP7 | Affected |
| SUSE Linux Enterprise Server 15 SP7 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP7 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP7 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP7 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP5 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP5 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP6 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP6 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP4-LTSS | Not-Affected |
| SUSE Linux Enterprise Server 15 SP4-LTSS | Not-Affected |
| SUSE Linux Enterprise Server 15 SP5 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP5 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP5-LTSS | Not-Affected |
| SUSE Linux Enterprise Server 15 SP5-LTSS | Not-Affected |
| SUSE Linux Enterprise Server 15 SP6 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP6 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP6-LTSS | Not-Affected |
| SUSE Linux Enterprise Server 15 SP6-LTSS | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP6 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP6 | Not-Affected |
| SUSE Manager Proxy 4.3 | Not-Affected |
| SUSE Manager Proxy 4.3 | Not-Affected |
| SUSE Manager Retail Branch Server 4.3 | Not-Affected |
| SUSE Manager Retail Branch Server 4.3 | Not-Affected |
| SUSE Manager Server 4.3 | Not-Affected |
| SUSE Manager Server 4.3 | Not-Affected |
| SUSE Enterprise Storage 7 | Not-Affected |
| SUSE Enterprise Storage 7 | Not-Affected |
| SUSE Enterprise Storage 7.1 | Not-Affected |
| SUSE Enterprise Storage 7.1 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP5 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP5 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP6 | Not-Affected |
| SUSE Linux Enterprise Desktop 15 SP6 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2-ESPOS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2-ESPOS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP2-LTSS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3-ESPOS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3-ESPOS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP6 | Not-Affected |
| SUSE Linux Enterprise High Performance Computing 15 SP6 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Module for Development Tools 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Affected |
| SUSE Linux Enterprise Real Time 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Real Time 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Real Time 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Real Time 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Real Time 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Real Time 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP2-BCL | Not-Affected |
| SUSE Linux Enterprise Server 15 SP2-BCL | Not-Affected |
| SUSE Linux Enterprise Server 15 SP2-LTSS | Not-Affected |
| SUSE Linux Enterprise Server 15 SP2-LTSS | Not-Affected |
| SUSE Linux Enterprise Server 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Server 15 SP3-BCL | Not-Affected |
| SUSE Linux Enterprise Server 15 SP3-BCL | Not-Affected |
| SUSE Linux Enterprise Server 15 SP3-LTSS | Not-Affected |
| SUSE Linux Enterprise Server 15 SP3-LTSS | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP2 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP3 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP4 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP5 | Not-Affected |
| SUSE Linux Enterprise Server for SAP Applications 15 SP5 | Not-Affected |
| SUSE Manager Proxy 4.1 | Not-Affected |
| SUSE Manager Proxy 4.1 | Not-Affected |
| SUSE Manager Proxy 4.2 | Not-Affected |
| SUSE Manager Proxy 4.2 | Not-Affected |
| SUSE Manager Retail Branch Server 4.1 | Not-Affected |
| SUSE Manager Retail Branch Server 4.1 | Not-Affected |
| SUSE Manager Retail Branch Server 4.2 | Not-Affected |
| SUSE Manager Retail Branch Server 4.2 | Not-Affected |
| SUSE Manager Server 4.1 | Not-Affected |
| SUSE Manager Server 4.1 | Not-Affected |
| SUSE Manager Server 4.2 | Not-Affected |
| SUSE Manager Server 4.2 | Not-Affected |
| openSUSE Leap 15.3 | Affected |
| openSUSE Leap 15.3 | Not-Affected |
| openSUSE Leap 15.3 | Not-Affected |
| openSUSE Leap 15.4 | Affected |
| openSUSE Leap 15.4 | Not-Affected |
| openSUSE Leap 15.4 | Not-Affected |
| openSUSE Leap 15.5 | Affected |
| openSUSE Leap 15.5 | Not-Affected |
| openSUSE Leap 15.5 | Not-Affected |
| openSUSE Leap 15.6 | Affected |
| openSUSE Leap 15.6 | Not-Affected |
| openSUSE Leap 15.6 | Not-Affected |
| suse/manager/5.0/x86_64/server suse/multi-linux-manager/5.1/x86_64/server suse/multi-linux-manager/5.2/x86_64/server | Affected |
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External POC / Exploit Code
Leaving vuln.today
GHSA-g7hg-vrcf-mvmr