CVE-2026-56820 Netty: Missing CertificateID Validation in OCSP Response Allows Replay Attacks
Attackers can bypass certificate revocation checks in Netty by replaying valid OCSP responses for unrelated certificates, undermining TLS security.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-56820?
CVE-2026-56820 is a high-severity vulnerability in Netty Netty, published on 21 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Netty is a network application framework for development of protocol servers and clients. In versions 4.2.0.Final through 4.2.15.Final and prior to 4.1.135.Final, `OcspClient` does not validate that the `CertificateID` in an OCSP response matches the requested `CertificateID`, which can lead to replay attack. `OcspClient.validateResponse` accepts a legitimately signed `GOOD` status response for an unrelated certificate issued by the same CA, allowing bypass of revocation checks for another certificate. This issue is fixed in versions 4.1.136.Final and 4.2.16.Final.
Weakness: CWE-295
Which versions are affected by CVE-2026-56820?
4 open source packages ship an affected version, including io.netty:netty-handler-ssl-ocsp. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-handler-ssl-ocsp Maven | All versions | 4.1.136.Final |
io.netty:netty-handler-ssl-ocsp Maven | All versions | 4.1.136.Final |
io.netty:netty-handler-ssl-ocsp Maven | From 4.2.0.Final | 4.2.16.Final |
io.netty:netty-handler-ssl-ocsp Maven | From 4.2.0.Final | 4.2.16.Final |
Products include Netty Netty.
How do I fix CVE-2026-56820?
Upgrade io.netty:netty-handler-ssl-ocsp to a fixed version for your release line: 4.1.136.Final or 4.2.16.Final.
Is CVE-2026-56820 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56820 exists.
Other vulnerabilities in Netty Netty
- CVE-2026-75595 Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
- CVE-2026-75596 Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing
- CVE-2026-59901 Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang
- CVE-2026-55851 Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion
- CVE-2026-56745 Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion
Sources
Also known as CLEANSTART-2026-CQ90755, CLEANSTART-2026-QT54780, DEBIAN-CVE-2026-56820, ECHO-eb30-6321-80ef, GHSA-272m-gcwp-mpwg, MINI-2pf9-hpqx-8qhp and 12 more.