CVE-2026-42582 is a high-severity allocation of resources without limits or throttling vulnerability in io.netty:netty-codec-http3 (maven), affecting versions <= 4.2.12.Final. It is fixed in 4.2.13.Final.
Summary When Netty decodes HTTP/3 headers, it sometimes runs new byte[length] using a length from the wire before checking that many bytes are really there. A small malicious header can claim a huge length (on the order of a gigabyte). Details When decoding header blocks, the non-Huffman branch of io.netty.handler.codec.http3.QpackDecoder#decodeHuffmanEncodedLiteral may execute new byte[length] for a string literal before verifying that length bytes are actually present in the compressed field section. The wire encoding allows a very large length to be expressed in few bytes. There is no check that length <= in.readableBytes() before new byte[length]. PoC The test below constructs a small HTTP/3 HEADERS frame whose QPACK section decodes to a ~1 GiB non-Huffman name length and is used to observe server-side failure; it illustrates how little wire data can target new byte[length]. Impact The server can slow down, stall, or crash under load when many crafted HTTP/3 HEADERS frames trigger very large byte[] allocations during QPACK literal decoding.
The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.
CVE-2026-42582 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (4.2.13.Final). Upgrading removes the vulnerable code path.
maven
io.netty:netty-codec-http3 (<= 4.2.12.Final)io.netty:netty-codec-http3 → 4.2.13.Final (maven)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter instead of chasing every advisory.
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Upgrade io.netty:netty-codec-http3 to 4.2.13.Final or later to resolve this vulnerability.
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2026-42582 is a high-severity allocation of resources without limits or throttling vulnerability in io.netty:netty-codec-http3 (maven), affecting versions <= 4.2.12.Final. It is fixed in 4.2.13.Final. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
CVE-2026-42582 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
io.netty:netty-codec-http3 (maven) versions <= 4.2.12.Final is affected.
Yes. CVE-2026-42582 is fixed in 4.2.13.Final. Upgrade to this version or later.
Whether CVE-2026-42582 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
Upgrade io.netty:netty-codec-http3 to 4.2.13.Final or later.