How severe is CVE-2026-42578?

CVE-2026-42578 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.

Is CVE-2026-42578 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (47th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-42578?

CVE-2026-42578 affects Netty. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-42578?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-42578 have an EU (EUVD) identifier?

Yes. CVE-2026-42578 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-30121.

When was CVE-2026-42578 published?

CVE-2026-42578 was published on 2026-05-13 and last updated on 2026-06-30.

CVE-2026-42578

CVE-2026-42578 is a high-severity vulnerability in Netty with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-113.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v4: 2.9
EPSS exploit prediction: 1% (47th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-30121
Weakness: CWE-113
Affected product: Netty
Published: 2026-05-13
Last modified: 2026-06-30

Description

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty's HttpProxyHandler constructs HTTP CONNECT requests with header validation explicitly disabled. The newInitialMessage() method creates headers using DefaultHttpHeadersFactory.headersFactory().withValidation(false), then adds user-provided outboundHeaders without any CRLF validation. This allows an attacker who can influence the outbound headers to inject arbitrary HTTP headers into the CONNECT request sent to the proxy server. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Frequently asked questions

What is CVE-2026-42578?: Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty's HttpProxyHandler constructs HTTP CONNECT requests with header validation explicitly disabled. The newInitialMessage() method creates headers using DefaultHttpHeadersFactory.headersFactory().withValidation(false), then adds user-provided outboundHeaders without any CRLF validation. This allows an attacker who can influence the outbound headers to inject arbitrary HTTP headers into the CONNECT request sent to the proxy server. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.
How severe is CVE-2026-42578?: CVE-2026-42578 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2026-42578 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (47th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-42578?: CVE-2026-42578 affects Netty. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-42578?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-42578 have an EU (EUVD) identifier?: Yes. CVE-2026-42578 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-30121.
When was CVE-2026-42578 published?: CVE-2026-42578 was published on 2026-05-13 and last updated on 2026-06-30.

References

Affected products (1)

cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:*

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