CVE-2026-59921

Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder

Published Jul 28, 2026 CVSS 3.1 · 5.7 Medium EPSS < 1% KEV · Not listed

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.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

netty

affected

Version	Status	Constraints
`>= 4.2.0.Final, < 4.2.16.Final`	affected	—
`< 4.1.136.Final`	affected	—

Configuration 1 [-]

OR	cpe:2.3:a:netty:netty::::::::
	cpe:2.3:a:netty:netty::::::::

No data.

No data available yet.

Remediation

No solution or workaround provided in the CVE record

Tracking

Advisories

Source	ID	Title
Github GHSA	GHSA-gcjf-9mgh-3p7g	Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder

Metrics

No CVSS v4.0

Attack Vector Adjacent Network

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact None

Integrity Impact High

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.465% probability within 30 days)

Exploitation poc

Automatable no

Technical Impact partial

References

Link	Providers
https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7g
https://nvd.nist.gov/vuln/detail/CVE-2026-59921
https://www.cve.org/CVERecord?id=CVE-2026-59921

History

Jul 29, 2026 1:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Jul 28, 2026 10:45 PM Description updated. Title updated View changes

Type	Values Removed	Values Added
Description	A flaw was found in Netty's HttpPostRequestEncoder, a widely used Java networking library component responsible for constructing multipart HTTP request bodies. The issue arises because user-supplied filenames and field names are directly embedded into Content-Disposition MIME headers without any validation or sanitization of CRLF (\r\n) characters. Since MIME headers are delimited by CRLF sequences, an attacker who controls the filename in a multipart upload can inject arbitrary MIME headers into the request body. This may lead to limited Content-Type spoofing or header manipulation against middleware or storage layers processing the request, though the practical impact is constrained by the context in which Netty is deployed.	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.
Title	io.netty/netty-codec-http: Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder	Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder

Jul 28, 2026 12:15 AM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
Description		A flaw was found in Netty's HttpPostRequestEncoder, a widely used Java networking library component responsible for constructing multipart HTTP request bodies. The issue arises because user-supplied filenames and field names are directly embedded into Content-Disposition MIME headers without any validation or sanitization of CRLF (\r\n) characters. Since MIME headers are delimited by CRLF sequences, an attacker who controls the filename in a multipart upload can inject arbitrary MIME headers into the request body. This may lead to limited Content-Type spoofing or header manipulation against middleware or storage layers processing the request, though the practical impact is constrained by the context in which Netty is deployed.
Title		io.netty/netty-codec-http: Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder
Weaknesses		CWE-93
References		https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7g https://nvd.nist.gov/vuln/detail/CVE-2026-59921 https://www.cve.org/CVERecord?id=CVE-2026-59921
Metrics	threat_severity `None`	cvssV3_1 `{'score': 5.7, 'vector': 'CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N'}` threat_severity `Moderate`