Vulnerability in io.netty:netty-handler-ssl-ocsp (CVE-2026-56821)
Summary
Vulnerability in io.netty:netty-handler-ssl-ocsp (CVE-2026-56821). Confidential information can be exposed externally. Exploitable via OcspServerCertificateValidator. Mitigation: upgrade to 4.1.136.Final or later.
Original description
The description as published by the source.
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OcspServerCertificateValidator flags an out-of-date OCSP response but does not stop processing it, so an expired GOOD response is still reported as VALID, letting an on-path attacker replay a stale GOOD response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ctx.fireExceptionCaught(new IllegalStateException("OCSP Response is out-of-date"));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
v…
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-56821 has been found in io.netty:netty-handler-ssl-ocsp.
Attackers can target a specific entry point like OcspServerCertificateValidator over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.4/10.
What to do: upgrade io.netty:netty-handler-ssl-ocsp to 4.1.136.Final or later.
If unsure, ask your IT team or search "io.netty:netty-handler-ssl-ocsp CVE-2026-56821" on the vendor's site.
CVE-2026-56821 (io.netty:netty-handler-ssl-ocsp) — CWE-299 / CVSS v3 7.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: OcspServerCertificateValidator / VALID / return / OcspValidationEvent
Patched: 4.1.136.Final — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-299) exists in io.netty:netty-handler-ssl-ocsp. Attackers reach the vulnerable code path via OcspServerCertificateValidator without authentication.
Check the vendor advisory for the affected versions of io.netty:netty-handler-ssl-ocsp. Attack surface: OcspServerCertificateValidator / VALID / return / OcspValidationEvent.
Severity: High (CVSS 7.4/10). Confidential information can be exposed externally.
Update to 4.1.136.Final.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで io.netty:netty-handler-ssl-ocsp を使っているサービスとバージョンを洗い出す。
-
2Apply patch patch
Upgrade io.netty:netty-handler-ssl-ocsp to 4.1.136.Finalステージング環境で 4.1.136.Final に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- exploit github.com
- web github.com
- web github.com
- web github.com