Executive brief
Netty is a widely used networking framework that helps Java applications communicate over the internet. A flaw in how it handles large data transfers allows an attacker to hide a second, unauthorized request inside a legitimate one. This can lead to 'request smuggling,' where an attacker bypasses security controls to perform unauthorized actions or interfere with other users' sessions.
Technical details
An integer overflow vulnerability exists in Netty's HTTP chunk size parser within the HttpObjectDecoder component. When processing chunked transfer encoding, the parser accumulates the chunk size using a 32-bit integer without sufficient overflow checks; specifically, it only checks if the final result is negative. By providing a carefully crafted hex chunk size (e.g., 100000004), an attacker can cause the parser to miscalculate the remaining data length. This allows a malicious actor to 'smuggle' a second HTTP request within the body of the first, which may be interpreted as a separate request by downstream servers or proxies. The issue is resolved in Netty 4.2.13.Final and 4.1.133.Final.
Affected products
- Netty netty-codec-http <= 4.2.12.Final, <= 4.1.132.Final
Timeline
- 2026-05-05: advisory: GitHub Security Advisory published
- 2026-05-13: disclosed: CVE published to NVD