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MEDIUM

CVE-2026-59921

CVSS v3

5.7

MEDIUM

EPSS Score

0.5 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • io.netty:netty-codec-httpMavenall versions · fixed in 4.1.136.Final

Vendor advisories

  • CVE-2026-59921 Red Hat Product Security2 products fixed · 57 known affected

    io.netty/netty-codec-http: Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder

    netty-codec-http as a component of Cryostat 4 · openshift-serverless-1/kn-ekb-dispatcher-rhel9 as a component of OpenShift Serverless · openshift-serverless-1/kn-ekb-receiver-rhel9 as a component of OpenShift Serverless

  • RHSA-2026:47172 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat build of Quarkus 3.33.2.SP3 security update

  • RHSA-2026:47189 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat build of Quarkus 3.27.4.SP3 security update

Full record on NVD

Description

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, HttpPostRequestEncoder constructs multipart HTTP request bodies by directly concatenating user-supplied filenames and field names into Content-Disposition MIME headers without validating or sanitizing CRLF characters (\r\n). Since MIME headers are delimited by CRLF, an attacker who controls the filename can inject arbitrary MIME headers into the multipart body part. The root cause is that neither the encoder nor the FileUpload implementations' setFilename() methods, which only check for null, neutralize CRLF characters before the filename is embedded into the header. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

Technical details

CVSS v3 Vector
CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
Published
2026-07-28
Last Modified
2026-07-29

Frequently asked questions

What is CVE-2026-59921?

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, HttpPostRequestEncoder constructs multipart HTTP request bodies by directly concatenating user-supplied filenames and field names into Content-Disposition MIME headers without validating or sanitizing CRLF characters (\r\n). Since MIME headers are delimited by CRLF, an attacker who controls the filename can inject arbitrary MIME headers into the multipart body part. The root cause is that neither the encoder nor the FileUpload implementations' setFilename() methods, which only check for null, neutralize CRLF characters before the filename is embedded into the header. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

Is CVE-2026-59921 actively exploited?

Active exploitation of CVE-2026-59921 has not been confirmed. Its EPSS score was 0.5% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-59921?

CVE-2026-59921 has a CVSS v3 base score of 5.7 (MEDIUM severity), with vector string CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N.

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