Unauthenticated request smuggling via chunk-size overflow
Published May 13, 2026 · Updated May 13, 2026
HTTP request smuggling in Netty 4.1.132.Final and earlier and 4.2.0.Alpha1 through 4.2.12.Final allows remote attackers to inject requests. HttpObjectDecoder#getChunkSize accumulates each hexadecimal digit in a signed int and rejects only negative results, allowing crafted oversized values to wrap to a valid positive chunk length. A network-reachable Netty HTTP server using the affected decoder can treat a second request inside the chunked body as a separate request; no authentication or user interaction is required.
Summary
What happened
HTTP request smuggling in Netty 4.1.132.Final and earlier and 4.2.0.Alpha1 through 4.2.12.Final allows remote attackers to inject requests. HttpObjectDecoder#getChunkSize accumulates each hexadecimal digit in a signed int and rejects only negative results, allowing crafted oversized values to wrap to a valid positive chunk length. A network-reachable Netty HTTP server using the affected decoder can treat a second request inside the chunked body as a separate request; no authentication or user interaction is required.
The record
- CVE
- CVE-2026-42580
- Published
- May 13, 2026
- Updated
- May 13, 2026
- Vendor
- The Netty Project
- Product
- Netty
- Classifications
- CWE-190, CWE-444, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 13, 2026CVE publishedPublication date reported by the CVE source.
- May 13, 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=< 4.1.133.Final
- Affected versionversion=>= 4.2.0.Alpha1, < 4.2.13.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
- Upstream chunk-size overflow proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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