Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, Netty's HTTP/2-to-HTTP/1.x translation layer (Http2StreamFrameToHttpObjectCodec and InboundHttp2ToHttpAdapter) fails to deduplicate or validate Host headers when an HTTP/2 client supplies both the :authority pseudo-header and a literal host header in a single HEADERS frame. The translator maps :authority to Host and separately copies the literal host header, producing an HttpRequest object containing two Host headers with attacker-controlled differing values. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.
CVE-2026-59900
MEDIUMPre-NVD 6.96.9—Trending — Patch released this week
EchelonGraph scoreMEDIUM confidence
This medium-severity CVE scores 6.9 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 79% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
Triggered by: NVD CVSS baseline
Sources: epss, secondary
6.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.9Exploit: None knownExposed: 0
A fix is available — apply it.
- CVSS v3
- 6.9
- EG Score
- 6.9(medium)
- EG Risk
- 36(Track)EG Risk 36/100SSVC: Track
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity69% × 45%Exploitation0% × 40%Automatability30% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 0%
- EPSS %ILE
- 21%
- KEV
- Not listed
Published
July 22, 2026
Last Modified
July 30, 2026
Advisory Details (3)
Auto-updated Jul 29, 2026Patch available. Sources: github, github_release.
github_release Patch Available
netty-4.2.16.Final
Patch available: netty/netty netty-4.2.16.Final
https://github.com/netty/netty/releases/tag/netty-4.2.16.Finalgithub_release Patch Available
netty-4.1.136.Final
Patch available: netty/netty netty-4.1.136.Final
https://github.com/netty/netty/releases/tag/netty-4.1.136.Finalgithub Patch Available
[codec-http2] Lack of Host Header Deduplication in HTTP/2→HTTP/1.x Translation Leads to Request Routing Bypass · Advisory · netty/netty · GitHub
https://github.com/netty/netty/security/advisories/GHSA-c69g-56f8-xwqjVendor Advisories for CVE-2026-59900(3)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- RHSA-2026:47172Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat build of Quarkus 3.33.2.SP3 security update
- RHSA-2026:47189Red Hat Product SecurityHigh
Red Hat Security Advisory: Red Hat build of Quarkus 3.27.4.SP3 security update
- GHSA-c69g-56f8-xwqjGitHub Security AdvisoriesMedium
Netty: [codec-http2] Lack of Host Header Deduplication in HTTP/2→HTTP/1.x Translation Leads to Request Routing Bypass
Patch Availability(1)
| Vendor / Ecosystem | Fixed in / Patch | Released | Source |
|---|---|---|---|
| redhat | netty-codec-http2 | 2026-07-30 | redhat |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Affected Packages
(1 across 1 ecosystem)
Maven(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| io.netty:netty-codec-http2 | 4.1.0.Beta4 ... 4.1.99.Final (148 versions) | 4.1.136.Final | — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 7× in last 7d / 9× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-30 16:47 UTCEG score recompute
- 2026-07-30 16:47 UTCVendor advisory
- 2026-07-30 16:28 UTCEPSS rescore
- 2026-07-29 18:31 UTCEG score recompute
- 2026-07-29 18:02 UTCEG score recompute▲ 6.90
- 2026-07-29 18:02 UTCMITRE cvelistV5CVSS v3 → 6.9 · CVSS v4 → 6.9
- 2026-07-29 13:46 UTCEG score recompute
- 2026-07-23 03:21 UTCEG score recompute
- 2026-07-22 22:27 UTCEG score recompute
Related CVEs(same vendor + same CWE)
Same vendor
10 shownredhat
- CVE-2001-0825EG 10.0HIGH
- CVE-2001-1009EG 10.0EPSS p93HIGH
- CVE-2001-0554EG 10.0EPSS p98HIGH
- CVE-2001-1162EG 10.0EPSS p96HIGH
- CVE-2001-0414EG 10.0EPSS p100HIGH
- CVE-2001-0191EG 10.0EPSS p92HIGH
- CVE-2001-0301EG 10.0EPSS p90HIGH
- CVE-2001-0197EG 10.0EPSS p96HIGH
- CVE-2001-0233EG 10.0EPSS p96HIGH
- CVE-2001-0010EG 10.0EPSS p98HIGH
Same CWE
10 shownCWE-444
Frequently asked(5)
What is CVE-2026-59900?
CVE-2026-59900 is a medium vulnerability published on July 22, 2026. Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, Netty's HTTP/2-to-HTTP/1.x translation layer (Http2StreamFrameToHttpObjectCodec and InboundHttp2ToHttpAdapter) fails to deduplicate or validate Host headers when an HTTP/2 client…
When was CVE-2026-59900 disclosed?
CVE-2026-59900 was first published in the National Vulnerability Database on July 22, 2026, with the most recent update on July 30, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-59900 actively exploited?
CVE-2026-59900 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 78.6% of all scored CVEs.
What is the CVSS score of CVE-2026-59900?
CVE-2026-59900 has a CVSS v3 base score of 6.9 (NVD).
How do I remediate CVE-2026-59900?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-59900, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-59900
Is Your Infrastructure Affected by CVE-2026-59900?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.