Request smuggling via forbidden chunk-extension line breaks
Published Mar 27, 2026 · Updated Mar 27, 2026
HTTP request smuggling in Netty through 4.1.131.Final and 4.2.0.Alpha1 through 4.2.10.Final allows remote attackers to inject requests. The HTTP/1.1 chunk decoder accepts forbidden CR or LF bytes inside quoted chunk-extension values and terminates the chunk start line at the embedded line break. Exploitation requires a Netty HTTP endpoint that processes crafted chunked requests; injected requests can bypass front-end controls or poison shared caches.
Summary
What happened
HTTP request smuggling in Netty through 4.1.131.Final and 4.2.0.Alpha1 through 4.2.10.Final allows remote attackers to inject requests. The HTTP/1.1 chunk decoder accepts forbidden CR or LF bytes inside quoted chunk-extension values and terminates the chunk start line at the embedded line break. Exploitation requires a Netty HTTP endpoint that processes crafted chunked requests; injected requests can bypass front-end controls or poison shared caches.
The record
- CVE
- CVE-2026-33870
- Published
- Mar 27, 2026
- Updated
- Mar 27, 2026
- Vendor
- The Netty Project
- Product
- Netty
- Classifications
- CWE-444, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 27, 2026CVE publishedPublication date reported by the CVE source.
- Mar 27, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 4.1.132.Final
- Affected versionversion=>= 4.2.0.Alpha1, < 4.2.10.Final
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Netty chunk-extension request-smuggling proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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