LowPublic exploit

HTTP Header Injection in Netty HttpProxyHandler CONNECT Requests

IdentifiersCVE-2026-42578CWE-113· Improper Neutralization of CRLF…

CVE-2026-42578 is an HTTP header injection vulnerability in Netty's proxy handling component, specifically io.netty.handler.proxy.HttpProxyHandler. In affected versions prior to 4.2.13.Final and 4.1.133.Final, HttpProxyHandler constructs HTTP CONNECT requests with header validation explicitly disabled in newInitialMessage(). The implementation creates headers via DefaultHttpHeadersFactory.headersFactory().withValidation(false) and then appends user-supplied outboundHeaders without CRLF validation. If an attacker can influence the outbound headers passed to HttpProxyHandler, they can inject arbitrary additional HTTP headers into the CONNECT request sent to the upstream proxy. The issue is effectively caused by improper neutralization of CRLF sequences in HTTP header data during proxy request construction.

For your environment

Are you exposed to this one?

Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.

Start free trial

ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows modification of the HTTP CONNECT request emitted to the proxy by injecting attacker-controlled headers. Depending on the surrounding application and proxy behavior, this can compromise request integrity and may enable security-relevant outcomes such as proxy authentication bypass, request smuggling-style manipulation at the proxy boundary, or unauthorized alteration of proxied connection metadata. The primary impact is on integrity of proxy-bound HTTP requests, though downstream effects depend on how the proxy interprets the injected headers.

Mitigation

If you can’t patch tonight, do this now.

Do not allow untrusted or user-controlled input to populate outboundHeaders for HttpProxyHandler. Apply strict validation and sanitization to header names and values, specifically rejecting CRLF characters and other input capable of breaking header boundaries. Where possible, enforce standard Netty header validation behavior rather than disabling it during CONNECT request construction.

Remediation

Patch, then assume compromise.

Upgrade Netty to a fixed release. The vulnerability is fixed in Netty 4.2.13.Final and 4.1.133.Final. Where code changes are feasible, ensure HttpProxyHandler does not construct CONNECT headers with validation disabled and that any outbound headers are validated before inclusion in the request.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

NettyNettyapplication

NettyNetty-Handler-Proxyapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

2 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

2 SOURCESView more in app

zeropath blogNews

Jun 12, 2026

Brief Summary: Netty SNI Handler Pre-Allocation DoS (CVE-2026-45416) Turns Nine Bytes Into 16 MiB of Memory Pressure - ZeroPath Blog | ZeroPath

Another Netty denial-of-service vulnerability mentioned only as part of vendor security history.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

Start free trial

Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity1