Cyber Resilience

CVE-2025-67735

Netty ≤ 4.1.129

Public PoC
Published
16 December 2025
Modified
02 January 2026
Patch / advisory
View advisory
CVSS Score v3.1 6.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
EPSS Score 0.0030 22th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2025-67735 is a medium-severity CRLF Injection (CWE-93) vulnerability in Netty Netty. Its CVSS base score is 6.5 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 22th percentile by exploit likelihood (below the median); 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-2 (Flaw Remediation) — 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. In versions prior to 4.1.129.Final and 4.2.8.Final, the `io.netty.handler.codec.http.HttpRequestEncoder` has a CRLF injection with the request URI when constructing a request. This leads to request smuggling when `HttpRequestEncoder` is used without proper…

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sanitization of the URI. Any application / framework using `HttpRequestEncoder` can be subject to be abused to perform request smuggling using CRLF injection. Versions 4.1.129.Final and 4.2.8.Final fix the issue.

CWE(s)
CWE-93

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

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 →
Why these techniques?

CRLF injection in public-facing HTTP encoder directly enables exploitation of vulnerable Netty-based applications for request smuggling.

Confidence: HIGH · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-42586Same product: Netty Netty
CVE-2026-41417Same product: Netty Netty
CVE-2026-50020Same product: Netty Netty
CVE-2026-42581Same product: Netty Netty
CVE-2026-42585Same product: Netty Netty
CVE-2026-42580Same product: Netty Netty
CVE-2025-58056Same product: Netty Netty
CVE-2026-33870Same product: Netty Netty
CVE-2026-42579Same product: Netty Netty
CVE-2026-44893Same product: Netty Netty

Affected Assets

netty
netty
≤ 4.1.129 · 4.2.0 — 4.2.8

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • SI-10 Information Input Validation
  • SI-2 Flaw Remediation
Detect
Catch it (NIST detect / respond)
  • SI-7 Software, Firmware, and Information Integrity
Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V4.2.4

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match
prevent

Directly requires validation and sanitization of untrusted input (request URI) to block CRLF injection before HttpRequestEncoder constructs the HTTP message.

SI-2 Flaw Remediation good match
prevent

Mandates timely application of the vendor patch (4.1.129.Final / 4.2.8.Final) that removes the CRLF injection flaw in HttpRequestEncoder.

SI-7 Software, Firmware, and Information Integrity partial match
detect

Requires integrity verification of software and data flows, enabling detection of smuggling attempts that result from unsanitized URI handling.

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 neutralization and validation to block 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
detects

Security testing can detect CRLF flaws but does not itself implement the neutralization.

A.8.25 Secure development life cycle partial match
prevents

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

A.8.26 Application security requirements partial match
prevents

Application security requirements include rules for neutralizing special characters such as CRLF in inputs.

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

Secure architecture principles encourage safe handling of untrusted data but do not prescribe specific CRLF controls.

A.8.28 Secure coding partial match
prevents

Secure coding standards explicitly require neutralization of CRLF sequences, fully addressing this weakness.

References