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VulnerabilityPublished Updated

CVE-2026-42581: netty · HTTP Request Smuggling

Affects nettySource GCVE Database

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Not known to be exploited · CVSS 5.8 Medium : upgrade to 4.2.13.Final or 4.1.133.Final when convenient.

Data as of 11 Nov 2026, 23:24 UTC

CVSS 3.1 base score
5.8Medium
How severe the flaw is on the 0–10 CVSS scale.

Sources agree

CVSS scores by source
CNA (GitHub_M)CVSS 3.15.8
ADP (redhat-SADP)CVSS 3.17.2
EPSS
0.6% chance of exploitation in 30 days – higher than 50% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 4.2.13.Final, 4.1.133.Final
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 13 May 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 11 Nov 2026.

What to do

Upgrade netty to 4.2.13.Final or 4.1.133.Final.

Affected software

ProductAffectedFixed in
netty nettyAffected
  • >=4.2.0.Alpha1 <4.2.13.Final
  • <4.1.133.Final
Fixed in
  • 4.2.13.Final
  • 4.1.133.Final

Description

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpObjectDecoder strips a conflicting Content-Length header when a request carries both Transfer-Encoding: chunked and Content-Length, but only for HTTP/1.1 messages. The guard is absent for HTTP/1.0. An attacker that sends an HTTP/1.0 request with both headers causes Netty to decode the body as chunked while leaving Content-Length intact in the forwarded HttpMessage. Any downstream proxy or handler that trusts Content-Length over Transfer-Encoding will disagree on message boundaries, enabling request smuggling. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

References

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