CVE-2026-59921
Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder
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.
INFO
Published Date :
July 28, 2026, 11:17 p.m.
Last Modified :
Aug. 7, 2026, 3:05 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | MEDIUM | MITRE-CVE | ||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update Netty to version 4.1.136.Final or later.
- Update Netty to version 4.2.16.Final or later.
- Validate and sanitize filenames in HTTP requests.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-59921.
| URL | Resource |
|---|---|
| https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7g | Mitigation Vendor Advisory |
| https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7g | Mitigation Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-59921 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-59921
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-59921 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-59921 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Reanalysis by [email protected]
Aug. 07, 2026
Action Type Old Value New Value Changed CPE Configuration OR *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.1.0 up to (excluding) 4.1.136 *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.2.0 up to (excluding) 4.2.16 OR *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions up to (excluding) 4.1.136 *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.2.0 up to (excluding) 4.2.16 -
Initial Analysis by [email protected]
Aug. 06, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N Added CPE Configuration OR *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.1.0 up to (excluding) 4.1.136 *cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:* versions from (including) 4.2.0 up to (excluding) 4.2.16 Added Reference Type GitHub, Inc.: https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7g Types: Mitigation, Vendor Advisory Added Reference Type CISA-ADP: https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7g Types: Mitigation, Vendor Advisory -
CVE Modified by [email protected]
Jul. 29, 2026
Action Type Old Value New Value Changed Affected [{'vendor': 'netty', 'product': 'netty', 'versions': [{'status': 'affected', 'version': '>=4.2.0.Final, < 4.2.16.Final'}, {'status': 'affected', 'version': '< 4.1.136.Final'}]}] [{'vendor': 'netty', 'product': 'netty', 'versions': [{'status': 'affected', 'version': '>= 4.2.0.Final, < 4.2.16.Final'}, {'status': 'affected', 'version': '< 4.1.136.Final'}]}] -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 29, 2026
Action Type Old Value New Value Added Reference https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7g Added SSVC {'id': 'CVE-2026-59921', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-29T12:49:35.429260Z'} -
New CVE Received by [email protected]
Jul. 28, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'netty', 'product': 'netty', 'versions': [{'status': 'affected', 'version': '>=4.2.0.Final, < 4.2.16.Final'}, {'status': 'affected', 'version': '< 4.1.136.Final'}]}] Added 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. Added CVSS V3.1 AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N Added CWE CWE-93 Added Reference https://github.com/netty/netty/security/advisories/GHSA-gcjf-9mgh-3p7g