Cyber Resilience

CVE-2026-42578

Netty ≤ 4.1.133

Public PoC
Published
13 May 2026
Modified
12 August 2026
Patch / advisory
View advisory
CVSS Score v4 2.9
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0095 58th percentile
Risk Priority 36 floored blend · peak EPSS

Summary

CVE-2026-42578 is a low-severity HTTP Request/Response Splitting (CWE-113) vulnerability in Netty Netty. Its CVSS base score is 2.9 (Low).

Operationally, exploitation aligns with the MITRE ATT&CK technique Content Injection (T1659); ranked in the top 42% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) and SI-15 (Information Output Filtering) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability Data

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…

more

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.

CWE(s)
CWE-113CWE-93

Related Threats

MITRE ATT&CK Enterprise Techniques

T1659 Content Injection Initial Access
Adversaries may gain access and continuously communicate with victims by injecting malicious content into systems through online network traffic.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2025-67735Same product: Netty Netty
CVE-2026-42586Same product: Netty Netty
CVE-2026-41417Same product: Netty Netty
CVE-2026-42581Same product: Netty Netty
CVE-2025-58056Same product: Netty Netty
CVE-2026-33870Same product: Netty Netty
CVE-2026-42585Same product: Netty Netty
CVE-2026-42584Same product: Netty Netty
CVE-2026-50020Same product: Netty Netty
CVE-2026-56817Same product: Netty Netty

Affected Assets

netty
netty
≤ 4.1.133 · 4.2.0 — 4.2.13

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V3.4.2
  • V4.1.3
  • V1.3.6
  • V4.2.3

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match

Input validation stops unneutralized CR/LF characters from being accepted and later emitted in HTTP headers.

SI-15 Information Output Filtering good match

Output filtering can neutralize CRLF sequences before they reach HTTP response headers.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require input sanitization and header handling that prevent CRLF injection.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development and acceptance can detect CRLF injection flaws before deployment.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle mandates input validation and output encoding that directly prevents CRLF injection into HTTP headers.

A.8.26 Application security requirements partial match
prevents

Application security requirements explicitly call for controls against injection flaws including HTTP header manipulation.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles reduce the likelihood of header-splitting vulnerabilities through proper component isolation.

A.8.28 Secure coding partial match
prevents

Secure coding standards require neutralization of CRLF sequences before inclusion in HTTP headers.

A.8.15 Logging none match
none

Logging of HTTP traffic can record header-splitting attempts, aiding detection and forensics.

References